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Aaron Gold

Can a better air filter improve fuel economy? We'll find out...

By May 18, 2006

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K&N air filterToday I got a couple of items for review from K&N Engineering. Horsepower-hungry car enthusiasts love K&N's high-flow air filters for the extra power they provide. I'm interested in seeing their effect on fuel economy. K&N doesn't officially claim that their filters boost fuel economy, though anecdotal evidence says otherwise. What they do say is that their filters effectively stay cleaner longer -- and a dirty air filter will cause a decrease in mileage. Paper filters, which most cars use, are supposed to be changed every 15,000 miles. The oiled-cotton K&N filter does its thing for 50,000 miles -- and instead of throwing it away, you clean it and reinstall it. So I'm going to give it a try. Over the next week I'll be logging the fuel economy of my wife Robin's Honda Accord wagon. Then I'll install the K&N filter they sent and we'll see what the differences are, both on my super-secret test loop and in Robin's everyday driving.

K&N Typhoon cold air systemK&N also sent a Typhoon cold air intake system. Cold air intakes are popular with gearheads because a) they look cool and b) they increae power. There is absolutely nothing cool about my wife's station wagon except the woman driving it, but power is definitely an issue. Robin hauls lots of heavy stuff day in and day out, and that means using every bit of power the Accord's 4-cylinder engine can muster. Honda didn't offer a V6 engine in the Accord wagon, but if they did I don't know if we'd want one. Oh, the car could definitely use more thrust -- but with gas at $3.35 per gallon, the last thing we need is another two hungry cylinders to feed. If the Typhoon can produce more useable power without an adverse affect on fuel economy, then I think it's time the gearheads stop keeping these things to themselves. Once we see what the K&N filter does, I'll install the Typhoon. Stay tuned to the blog for updates. -- Aaron Gold

May 18, 2006 at 2:21 pm
(1) Dick Brewster says:

New car “paper” filters don’t generally need to be changed every 15,000 miles unless you believe K&N’s propaganda.

K&N filters also don’t filter as well as the stock “paper” filters. Whether that actually makes a difference depends on your driving conditions and who you ask.

Hold a K&N filter up to the light and you can see holes in it. No matter what the propaganda says, dirt doesn’t have a magic guidance system that causes it to avoid the holes and commit suicide on the oiled cotton in the K&N. If a dirt particle is lined up with one of the many pinholes in a K&N, it will go through the hole.

K&N drop in substitue aur filter elements also don’t generally increase power. Many dyno runs by car enthusiasts have shown that on many cars.

You need to change the filter housing to get a power gain because the housing is where the restriction is on most cars, not the element.

May 18, 2006 at 2:27 pm
(2) Dick Brewster says:

I just checked the owners manual for my new Chevy (C6 Corvette). It calls for an air cleaner element replacement at 50,000 miles, not 15,000 miles as stated in the article.

April 14, 2011 at 10:52 am
(3) Steve says:

Probably because you already have a Factory Installed K&N “type” of Air Filter…like by 2008 Focus had…check every 50,000 (Ford cleans it if needed then) Soooooooooo, K&N’s “propaganda” as you call it is more than likely true. Also, dirt is attracted to cotton…and oil is a very sticky element for even the tiniest dust particles to stick to. You must for another “aftermarket” filter company. :)

May 18, 2006 at 3:06 pm
(4) Dale Brannigan says:

Filter replacement times vary by vehicle, vehicle use and intake setup. The paper filter in my Jeep Liberty was horrifically fouled at 15k miles. The K&n marketing materials say 97-99% removal efficienct of 10-20 micron particles, I couldn’t find any information for paper elements. Paper elements must have holes too, else they’d be air blockers not filters.

April 24, 2011 at 8:01 pm
(5) m.carnes says:

no they vary by the amount of dust in the air /as in if you do off road driving or have a gravel road you travel etc.

May 18, 2006 at 4:34 pm
(6) Aaron Gold - Cars Guide says:

Dick, is the air filter in your Corvette a paper-element filter?

May 18, 2006 at 10:17 pm
(7) Jeff Thomas says:

I just bought a new Toyota Tundra and installed a K&N fliter. I’ve been driving it for just over a month and it feels like I’ve gained some power, but I haven’t noticed an improvement in MPG. I have been driving conservatively.

May 19, 2006 at 1:14 pm
(8) Dick Brewster says:

Aaron, yes, it is a “paper” element.

If you can get someone to spring for the money, back to back chassis dyno tests with a clean stock element, a drop in K&N element and the Typhoon on your wife’s Honda would add a lot to your blog and article. Chassis dyno runs aren;t terribly expensive and you might get someone to run them for free just for getting mentioned in an article.

Dale, yes “paper” elements have holes too, the difference is that they are small enough that you can’t seee them when you hold the filter up to the light. The holes in a K&N are big enough to see. Try it.

A K&N is around 97% effective, a good paper element is over 99% effective. That means the K&N is passing over 3 times as much dirt. Whether that is problem for the average owner of not is a good question. I prefer to minimize the amount of dirt that goes into my engine, particularly when dyno tests usually show that a K&N in the stock filter housing usually make no to very little improvement.

March 28, 2011 at 10:58 am
(9) Jesus says:

Dick, k&n air filters do give you a slight bit more BHP as it drags in more air than a standard pile of sh*t you use. Paper filters wear out quickly as there constantly getting battered by dirt. K*n have oil-cotton ‘strips’ which gets rid of up to 98-99% of dirt on contact, and lasts much longer =) no way are standard filters better than k&n with proper housing.

May 19, 2006 at 3:12 pm
(10) aaron Gold - Cars Guide says:

Dyno runs are an interesting idea, though my biggest concern is real-world fuel economy. K&N claims the Typhoon gives a 6 hp increase at high RPMs for the Accord (that’s around 4%), but HP isn’t what I’m interested in power-wise — it’s torque. So I’m going to use the very un-scientific method which I believe enthusiasts call “the butt dyno”. Robin drives the car with the same load up the same hills every day. If there’s a real-world power increase, she’ll feel it.

Dirt is, of course, a very important issue. I talked to one of my sources that uses K&N filters as part of their power kits for pickups and motorhomes, but they do not do filtration tests, though being an aftermarket manufacturer they are always concerned with warranty claims.

I found a couple of articles on K&N filtration. This one from their FAQ talks about filtration standards. This one from a dealer talks about how the filtration media works vs. paper. Forgive me, I’ve only had time to skim these — let me see if I can get K&N’s take on this.

Your questions are valid, Dick; obviously engine protection is the primary goal of a filter, else the car wouldn’t need one. I appreciate the continued comments and am going to dig into this more.

May 19, 2006 at 4:59 pm
(11) Tim says:

Is there even one auto manufacturer that uses one of these high-performance filters? I’m talking about the oiled-cotton or oiled-foam type filters such as K&N brand filters. I can’t think of any. Don’t you think GM would take advatage of gaining such cheap horsepower in cars like their Corvettes or GTO, or Chrysler in any of their HEMI powered cars? Not even Ferrari or Lamborgini uses such a filter. The reason they don’t is because these filters don’t really filter dirt that well and engine wear is terrible with these filters.

I recall reading an article in an industry-specific magazine where a team of industrial engineers for a large construction company was trying to find ways to save money on equipment maintenance. One large expense the company wanted to cut was it’s expense on air filters for all the machinery. Air filters for the large trucks and earth movers cost in the $100-$500 range and they had to be changed weekly on many of the machines. The engineers decided to try the reusable oiled-cotton and foam type filters to save money. Because these machines are so expensive, the company takes weekly oil samples to catch potential problems with the engines. When they started using the reusable filters the oil samples began reflecting a significant increase in metals in the samples indicating engine wear. It was so bad they had to stop the tests after only 4 weeks.

Maybe you will get an additional mile-to-the-gallon with these filters, but you need to ask, why don’t the manufacturers use these filters for the same reason? Horsepower and gas mileage figures are such huge selling points and the manufacturers don’t take advantage of such a cheap way to boost their figures, why? They’re not good for the longevity of your engine.

Leave your paper filter in for 50,000 miles and you could build a nice clay ash-tray in your pottery class with the dirt you extract from it. Like a previous person say, the dirt doesn’t evaporate when it hits the K&N filter, much of it gets through and slowly sands down your engine.

January 19, 2011 at 1:01 pm
(12) gerard says:

for these big machines they should go back to the 60″s and before for the oil bath air cleaner where you just clean the wire mesh and and fill up with less than 1qt of oil.

May 7, 2011 at 3:14 am
(13) Nam says:

I read a lot about these things (filters) and I must say that I agree with you 100%…A lot of times people just believe what has been said about K&N filters but don’t do the research themselves. It all comes down to whether they want a little better gas mileage and horse power or let their engines ruined. Just like “Every good drug has its side effects, even Viagra!”

October 7, 2011 at 10:43 pm
(14) Anthony says:

Everbody have their own decision, for good economic back ground off cause will choose for K&N product.
But if you no money, just using temporary “paper filter” loh. Is better don’t comments too much…

May 19, 2006 at 5:13 pm
(15) Aaron Gold - Cars Guide says:

Well, I do know why the automakers don’t generally install these filters as OEM equipment; this used to come up when I worked as a writer for Banks Engineering. It comes down to cost vs benefit. Cars are engineered to a price. If they lose $10 per car in profit on a Corvette, that’s around $300k for a year’s production run. Adding $10 to the cost of a Camry would cost Toyota around $4 million.

But — I don’t want to come across as an apologist for K&N; I’ve just answered the cost question so many times I can do it in my sleep. (When you get into modified intakes, you add production complexity as well as parts cost. Don’t get me started… er, wait, it’s too late!)

The filtration issue is, as I’ve said, very valid. We’ll see what K&N has to say.

May 19, 2006 at 6:05 pm
(16) TIm says:

I knew the cost point would be brought up, that’s why I included exotic car makers in my question of why don’t they use these filters. I know of no manufacturer, not one, that uses these filters. Even the manufactureres that build their cars for exotic performance like the Ferrari, Lambo, AMG, BMW M, Saleen, Roush, and Ruf.

I think they decline using these filters because their engines won’t last with the poor filtration. Either that or they don’t really have the horsepower gains they claim.

May 19, 2006 at 9:03 pm
(17) rog says:

Geez, can’t wait to trash my oiled K&N filter as soon as AMSOIL makes one of their nano-fiber filters to fit my Vibe. They claim 100% efficiency …

May 19, 2006 at 10:08 pm
(18) cars says:

Hi everyone – David Vespremi, brand marketing director at K&N, posted a detailed comment; because of the length, I have moved it to our Forums.

To read David’s comment, go here (or, to do it the long way, go to http://cars.about.com/mpboards.htm, General Discussions, K&N Filters). Make sure to hit “view full message” at the bottom to get the last paragraph or so – like I said, it was a detailed comment! :)

Thanks, David, for taking the time to reply, and thanks everyone else for reading and commenting — I look forward to seeing your replies to David’s post. – Aaron

May 20, 2006 at 12:49 am
(19) Tim says:

I can appreciate Mr. Vespremi position as to why auto manufactures do not use oiled-cotton (re-useable) air filters. He’s the marketing director at K&N. I’m not going to suggest that he told you anything untrue in his statement either. I’m quite sure dealerships and OEM manufacturers make money when you go back to the dealership to buy replacement parts. I’m also confident that K&N filters will be used quite successfully in motor sports. But I do dispute his points as to why manufacturers of high-performance vehicles do not use reusable, oiled cotton air filters.

He said manufacturers use filter replacement as a steady flow of cash for the dealerships and OEM suppliers. The dealerships could just as easily charge you for the cleaning kit that’s required to clean and re-oil your air filter i.e. K&N’s Recaharger filter care service kit. Explain 100k mile iridium spark plugs, 100k-150k mile radiator coolant, sealed transmissions that never require oil changes if manufactures are trying to keep you in the dealership service departments. Maybe it’s clear to him that manufactures use paper filters as a profit center but with manufactures where horsepower and performance is king, I’m not agreeing with that point.

Another point he makes is K&N’s use in motor sports. I doubt piston ring and cylinder wall wear from poor air filtration is ever a problem after 500 mile races…even 1000mile baja races through the desert. To a race team, every horsepower counts and I’m sure oiled-cotton filters are better than paper filters hands down.

I not trying to trash K&N filters, just don’t expect them to filter dirt as well as a OEM filter.

May 20, 2006 at 10:02 am
(20) Dale Brannigan says:

The problem with the butt dyno is the user tends to conclude what they had already thought going in. Take acetone as an example, people that use it claim that it makes a huge difference, but if you make a measured controlled test it doesn’t do anything (at best). Dick, i haven’t found anything claiming 99% efficiency for paper filters (and fyi good job twisting my comment, K&N claims 97-99 depending on filter shape and intake setup, not straight 97%), and like you said at what poing does particle size make a difference. Personally I’ve never noticed a significant mileage or performance benefit maybe 1-1.5 mpg, I prefer oiled cotton for convenience sake, pay once up front, clean when dirty. There are an awful lot of claims about articles being read here but i don’t see any links. I read once that if i pour sand down my intake with the engine running it’ll port and polish my heads! No really I did.

May 20, 2006 at 2:26 pm
(21) michael says:

i have a 2005 xterra my paper filter will clog up at about 10,000 miles and my gas milage goes down alot, so i change it,, anyone who thinks a filter will last 50,000 miles must live in a clean room, i have thought of buying the intake kit from k&n to boost power,my question is, will the vortec cyclone be a better choice ,im happy with the paper filter

May 20, 2006 at 3:08 pm
(22) Aaron Gold - Cars Guide says:

I always got the impression that the Vortec Cyclone, the Turbonator and things of its ilk were scams. I will see if I can get one to test out — you never know.

May 20, 2006 at 5:39 pm
(23) michael says:

Aaron,thanks i would like too find out about the vortex ,it does sound practical on their wed site ,but many things do ,so far my xterra has been very good 20 mpg has been normal but i drive 75 & 80 mph too work 5 days a week 80 mile round trip , but i like power so any increase in hp or torque is a plus thats the biggest reason i might consider the k&n system ,michael

May 20, 2006 at 7:56 pm
(24) Dick Brewster says:

Aaron, regarding price sensitivity being areason why manufacturers don;t use K&N type filters. You argument sounds good, but:

1. Car manufacturers would kill to get the economy improvements K&N claims. The price of a K&N element is insignificant compared to the value of increassing their fleet mileage. K&Ns fuel economy claims have some merit if you are driving a carbrueted car (remember those?). If you are driving a modern fuel injected car, the system adjusts the mixture to compensate for a reasonable amount of filter restriction so there is very little if any change in economy with filters of different restrictions.

2. Look to the world of multi-million dollar off road military vehicles and big $$$ construction equipment. They don’t use K&N type filters because they don’t work as well as “paper” type element filters. Their engines are very expensive and downtime is very expensive for them

May 20, 2006 at 10:54 pm
(25) Aaron Gold - Cars Guide says:

Michael: I know this isn’t the answer you’re gonna want to hear, my man, but the best way to improve your MPG is to slow down. As speed rises, fuel consumption rises exponentially, largely due to wind resistance — which the XTerra has in droves.

Dick — Did you read David’s forum post? You really should. K&N doesn’t make any claims that their filters increase fuel economy. They let others, mind you, but they don’t.

May 21, 2006 at 12:57 am
(26) Dick Brewster says:

Michael, they do claim fuel economy improvements. Read K&Ns own FAQ


May 22, 2006 at 1:53 pm
(27) J Kyle says:

I’ve been well aware of K&N’s products before but hadn’t thought too hard about them, mostly because I’m too cheap. From the reading here, I’m afraid that they’re starting to go down in my eyes – and while it’s nice to have a post from a K&N marketer, I feel that it did more harm than good.

The “fuel economy benefits” seem to be from a clogged 10k paper filter vs a new K&N filter. I suspect that the people who don’t bother to change their paper filters will be unlikely to clean their K&N filter, especially since it sounds somewhat messy (rinsing, oiling) compared to the simple yank-the-old slap-in-the-new paper filter replacement.

The “revenue stream” theory is an insult to our intelligence, plain and simple. If this were truly the case, we’d still be dealing with carbs and grease fittings (and someone already mentioned the long-life spark plugs, fluids, etc.) This is no different that criminals like Kevin Trudeau claiming that you can’t trust medical science because the doctors would rather have you sick and coming back for more treatments. I’d also point out that some factory wear parts (first-hand knowledge points specifically to clutches) last significantly longer than the bssic aftermarket parts.

As for racing – racing teams use them because K&N pays for them to use them. It’s as simple as that. You could also note that some forms of racing use no filtration, or something simple like a metal mesh or an oil bath.

And Aaron, I’ll agree with Dale – anectodal evidence (ie, even a properly calibrated buttdyno) is completely useless. Even if you wanted to use first-hand observations, you and Robin aren’t enough people to do double-blind testing! (Need at least a tester, testee, and another making the changes.) You need quantitative, repeatable measurements to get usable results.

May 22, 2006 at 2:46 pm
(28) Aaron Gold - Cars Guide says:

I’ve decided to move David’s post back out here to the comments section. Here it is…

May 22, 2006 at 2:47 pm
(29) David Vespremi says:

I’d like to make myself available for questions and comments on this article. I am the Brand Marketing Director at K&N Engineering, Inc. I am also an automotive enthusiast and published automotive author (“Car Hacks and Mods for Dummies, Yahoo!, and TechTV included)

As such, I can help address some of these questions and concerns as both a knowledgeable enthusiast who has used K&N on various project cars well before I worked for the company, and now most recently, as a representative of K&N.

I am pleased to have been asked to contribute to this dialogue and appreciate the interest in K&N’s products. I am further grateful to Aaron for taking the opportunity to provide his readers with objective feedback – be it good or bad – about our products. At K&N, we are proud of the fact that we make the World’s Best air filters and intake systems – manufactured in Riverside, California for over 37 years by enthusiasts. To date, over 15 million K&N air filter are in active use worldwide and K&N is one of the few, if not only, companies with a full ISO/SAE filtration lab on site that allows us to continually benchmark our products in every step of the development process. This includes the “three legged stool” of criteria by which we measure our filters’ performance: (1) filtration – the ability to prevent harmful contaminants and particulate matter from getting into the engine (2) flow – the ability to get air to the engine and (3) dirt retention – the ability to perform these over the longest service life possible without a degradation in performance. It is in achieving the “sweet spot” between these three that makes a K&N a K&N.

While it is true that there are filters that stop more particulates than K&N, and that there are those that flow more air, as there those that retain more dirt before degrading in performance, it is K&N’s mission to excel not in any one category – but as a compromise of all three – and to do this with a filter that has a service life for the entire life of your car.

I should further point out that K&N makes no claims that our products improve fuel efficiency. Even the EPAs mandated numbers for OEMs are just estimates, so any estimated improvements on what is itself an estimate is a bit of reach. What we can conclusively say is that under a Department of Energy Report, a clogged air filter can negatively impact fuel economy by up to 10% and that there is a relatively high number of vehicles on the road using paper filters past a point in which fuel mileage is likely being impacted. By using a K&N (or any new filter) that fuel mileage can be restored. The critical difference and primary point of appeal for a K&N Lifetime filter over the disposable variety is that unlike a paper filter, a K&N Lifetime filter never needs to be replaced. As such, the money and hassle you save with K&N as compared to continually buying and replacing paper filters can be avoided. Further, because over 100 million disposable air filters and their associated packaging end up in landfills in the U.S. alone each year, K&N helps reduce the waste associated with the manufacture, transport, and use of these disposable products.

To address the question of why an OEM manufacturer would not be inclined to equip cars with K&N from the factory, one has to look at the business model behind building, selling, and servicing cars. Why do many car manufacturers now offer 10 year 100k warranties? The reason is simple. The cars are well built enough to last that long, but by keeping customers coming back to dealerships for consumables, which includes everything from brake pads and rotors, to spark plugs, to oil changes – and yes – filter changes, the manufacture can build into the target price of every car sold a profit center to subsidize the price of the car.

It is no different from how before the days of bagless vacuum cleaners, a vacuum cleaner would be sold with very little profit margin since the bags themselves would need to be continually repurchased, or why coffee machines were once sold with paper filters specific to the shape and size of that machine before the standard switched to lifetime metal filters. It is a form of planned obsolescence, and one that is against the core philosophy of how K&N engineers its products.

It is clear that paper automotive filters work are a profit center pure and simple. As it is now, K&N is a large global company selling millions of filters a year. Think of how many more a company like ours could sell if we sold more than one per vehicle. However, our value proposition to the consumer is very different and consumers know that while our filters cost a bit more up front, they have the peace of mind from knowing that they are getting the very best for their cars.

To support this, K&N has, of course, been use in Motorsports for many years. This includes Indy Car – every car that crosses the finish line at next week’s Indy 500 will be using a K&N – Champ Car, NHRA, WRC, NASCAR, Baja 500 and 1000, all the way down to the most obscure grassroots forms of motorsports. For those inclined to think that a K&N does not stop dirt, ask a Baja racer some time why they don’t simply elect to use paper filters? Obviously, they must be concerned about the fine silt and dirt getting into their engines in the 1,000 mile desert race.

However, I am not here to extol the performance benefits of a factory replacement filter. Yes, it flows more air than a paper filter – those who have seen K&N’s air flow demonstrators (the ones that use the ping pong ball) in retail environments know this to be true. But because it flows more air, or because light is visible through the pleats, doesn’t mean that a K&N doesn’t excel under SAE/ISO tests under our three-legged stool criteria.

The reason for this is simple, K&N works on an entirely different physics principle than a paper filter. You see, a paper filter stops dirt by presenting a barrier full of pores that fill up with dirt as it accumulates on the filter’s surface. The fewer unclogged pores remain available, the less air the filter is able to pass through to the engine. This is called surface loading. A K&N filter depth loads, meaning that the particulates are held in suspension by a tacking agent. Since the contaminant particles essentially becomes a magnet for other particles, the particles build up on each other into bigger clumps and the air continues to flow around them through the grid matrix weave of the cotton fibers. This is called depth loading.

For those that want performance – a guaranteed increase in horsepower that you can actually feel – K&N offers our performance intake systems. These are significantly more expensive than the Lifetime replacement filters, but their quality and performance are second to none. While our Lifetime filters do outflow paper filters, it is only after eliminating the maze of factory baffles, chambers and plumbing that our Intake Systems provide that an uncompromised increase in performance can be released.

I’ll cut this short for now, but I am happy to answer questions here so please feel free to fire away.

David Vespremi
K&N Brand Marketing Directo

May 22, 2006 at 3:17 pm
(30) David Vespremi says:

I would like to address some points raised by J Kyle:

(1) A K&N will never need to be serviced for as long as the average person owns a car, so your point about the hassle of servicing is a bit off. Consider that the inspection interval – not cleaning – is between 50-70k for replacement filters and 70-100k for Intake systems. This is when you first take a look and see how the K&N is doing – not when you must clean it. Recently, we had the opportunity to test our CEO’s Intake System from his Lexus after 137k miles – with no cleanings. This product still flowed far more air than a paper filter, and showed only a small percentage of flow restriction as compared to brand new K&N. We saw similar results after testing the Around the World filters that a team of Land Rovers used driving 44,000 miles around the globe.

Further, even if the product needed cleaning upon inspection, it can be done for you at EZ Lube (authorized K&N sales and service) or a similar service center. There is no question that a typical paper filter will clog and restrict air flow before a K&N. This truly is not a gray area.

(2) The revenue stream is very real. How much do you think a paper filter costs an OEM vs. how much is charged for this item (parts and labor) to the end consumer? Do you think, for example, that the $30 a consumer is being charged at a dealership for an air filter replacement is commensurate with the cost of that product and service? How does this compare with the $30 Lifetime K&N product for value?

(3) The race team allegation is untrue. While K&N does pay for title rights to a series or event, as well as contingency sponsorship for racers who win racers using our products, we do not sponsor a racer or even in which our product is not in use. Further, as a rule, racers, crew chiefs, and engine builders campaign cars to win races. No amount of sponsorship money is going to convince a competitive team to run a product that will cause them to either risk not winning or incur additional expense over what the sponsorship brings them. Speculating that a team would risk an engine costing tens or hundreds of thousands of dollars because a company like K&N might pay them a small contingency prize if they win is a bit off. The math just does not work out in the team’s/racers favor.

I hope this helps clarify some of these items. I really don’t intend to come across as argumentative, but as an “insider” it is interesting how much folklore there is around some of these issues.

May 23, 2006 at 11:59 am
(31) J Kyle says:

The revenue stream idea is, as I said, absolutely insulting to our intelligence and it reflects poorly on K&N to keep bringing it up.

If you’d like to say that it’s a premium product and that manufacturers are trying to bring in a car as inexpensively as possible, that’s a valid point. But with modern cars coming with long-life spark plugs, fluids, chassises that don’t need greasing, and are recommending oil changes at 7,500 or more miles… then your claim that they don’t use long-life air filters simply to keep you coming back for service looks completely laughable. If manufacturers had air filters available to them that lasted for 100k between changes instead of 15k, they’d use them. Heck, even the synthetic oil folks got a couple manufacturers to use their stuff!

As for racers… well, I sort-of take it back if you’re not actively sponsoring racers, but I think it’s generally fair to assume that when one sees a K&N sticker on a competition car, that K&N has paid to have it put there. Contigency is probably more sensible from a business standpoint, you can get lots of people to put the sticker on without actually paying some of them – that’s why we see so many “Tire Rack” sunshades on autocross cars! :)

Don’t get me wrong – I’m not on some K&N hatefest. I would certainly still considering using a filtercharger (though I would do some more research first) and would probably be happy to put one of the cold air intake systems on my STi, but again, I’m too cheap and I have an old Lotus that soaks up all my spare automotive funds!

But much of this is pure tangent. The point of Aaron’s original message is MPG and nothing else. The question is, can a K&N filter improve mileage over a new, clean paper filter? I’m not sure that it would – in fact, I would guess that, theoretically, an increase over the stock amount of air coming in would mean the FI computer slightly increasing the amount of fuel to avoid running lean – which would mean more power, but more gas being used, which would probably counter any savings from the intake not having to use as much energy inhaling.

May 23, 2006 at 12:09 pm
(32) joe scanlon says:

Hi;cant help adding my two cents worth in here.i have been using a k & n filter
on my 87 dodge diplomat now for about a year.can.t say that it really helped all that much.but what did really help was putting six pairs of ceramic block magnets on the fuel line close to the carburetor as possible.north pole to north pole.they must reject each other.
this dodge will now run on 87octane with no detonation with ac on climbing the steepest mtn,s.somthing it would never do before even with 93octane gas.gas mpg gained about 2.5 on the hyw,y.the bad news is they don,t work on my fuel injected ford or fuel injection for that matter.they will work on gravity feed lawn mowers & snow blowers.fuel injection pressures are too high.try them on your old cars,you will be supprised like i was.go on google,check out “eureka magazines comments on fuel line magnets.also check.”what too do with old computer magnets”.they have also been used on gas burners.have fun
Joe S.

May 23, 2006 at 2:59 pm
(33) Aaron Gold - Cars Guide says:

More on the wear issue: I called my friend Alan, owner of The Polishing Shop in Thousand Oaks, CA. Alan ran a successful engine-rebuilding shop for many years. He said that most of the instances of premature wear he saw were on engines where the air filter and other routine maintenance items were neglected. The engines coming in for “routine” rebuilds after 200,000 or more miles were those that had been kept up, and he did not see any significant difference in wear between cars that used paper filters and those with K&N or other oiled-cotton-type filters. He likes the K&N filters and recommends checking them at the recommended interval for paper filters (around 12,000 miles) and cleaning them as necessary, generally at every other inspection.

May 23, 2006 at 8:59 pm
(34) Dick Brewster says:

David Vesprimi of K&N wrote:

(1) A K&N will never need to be serviced for as long as the average person owns a car, so your point about the hassle of servicing is a bit off. Consider that the inspection interval – not cleaning – is between 50-70k for replacement filters and 70-100k for Intake systems. This is when you first take a look and see how the K&N is doing – not when you must clean it.

David, please don’t insult us with that nonsense and go talk to your “engineering” department. It sounds like you have K&N’s guaranteed filter life of 1,000,000 miles mixed up with the service interval.

K&N’s website recommends a much saner 30,000 to 50,000 miles for cleaning with inspection on an annual basis.


May 23, 2006 at 9:33 pm
(35) David Vespremi says:


The website is undergoing updates and revisions as we speak and I am working closely with our engineering staff to rewrite portions of it. The result of this discussion has helped identify some areas that badly need to be revisited. Your pointing me to these links is very helpful.


June 3, 2006 at 2:45 pm
(36) Shon Barrett says:

“Depth loading” is not a optimal way to filter particles. Just research the sharper image air cleaners that use electical charge in much the same way as K&N uses oil. When it comes to filtration there is no substitute for a paper filter. Every clean room, hospital and microchip company use one form or another to keep the air clean. You expect me to believe that Honda didn’t use your filters on my Accord because of service revenues? Do you understand that the factory recommended oil change interval for my car is 15,000 miles yet I see mobile one commercials advertising 5,000 mile oil! I understand that this has to do with my vehicle but still…. They want to sell oil, you want to sell filters, honda wants to sell reliable cars. I have been following this conversation and again and again I think David misses the key points here. I am not going to argue that a K&N is a performance leader. Don’t give us that motorsports talk. The small size of particles that we are talking about are not going to make a difference in your typical nascar race. We are talking about long term wear. If cotton based filters were that much of an advantage then ferrari would use them on their cars, in formula 1, on everything. Do you know how manufactures increase the performance of their “inferior” air filters? Give them move filter surface area. This is all about making less resistance to air rushing into the cylinder to equalize the pressure drop created when the piston falls.
It all comes down to this. I change my oil, I do my maintanence and I want my car to last as long as possible, so I choose paper. Why would I compromise to pick up a few horse power? They aren’t going to make the difference. A new filter is not going to make your car “fast.” If it wasn’t for sponsorship I am pretty sure several forms of racing wouldn’t even use a filter.

To make this point even better, look at what major trucking companies use. Every mpg counts, every dollar counts and performance counts. UPS uses paper and they change them regularly. Why wouldn’t they use cotton based cleanable ones on their vehicles? It would save money. They clock 500,000 miles on their engines all the time, wouldn’t they use them if they were more effecient yet lasted a lifetime?

June 3, 2006 at 2:48 pm
(37) Shon Barrett says:

I meant to say – I am not going to argue that K&N is not a performance leader.

June 5, 2006 at 5:01 am
(38) Kinch says:

Ok, i tried the K&N filter for my 96 Accord and the Honda stock OEM filter. I don’t see any difference at all between the two. I do not notice HP increase (maybe K&N’s mind trick made me into believe a 1 or 2 hp increase) nor any MPG increase, so K&N obviously is playing that advertising trick to lure people into spending money to get their highly hyped oiled filters. Anyway, I am very disappointed as my hard earned 36bucks went to K&N’s profit, so i hope people out there will be more aware of the fact that K&N filter do not perform as advertised!!!

June 5, 2006 at 10:35 am
(39) DavidV says:

Shon and Kinch,

The value of the K&N, as I have previosuly stated in this thread, is that it never needs to be replaced. This means money savings over continually replacing disposable filters, it means waste reduction when considering the 100 million air filters that end up in land fills each year, and it means convenience – one less thing to worry about as compared to the time and effort spent staying on top of paper filter changes.

Hopefully, you’ll enjoy the value of your K&N’s for these reasons. If it is horsepower you crave, I would highly recommend that you consider a K&N Performance Air Intake Systems. These come with a gauranteed increase in horsepower you can actually feel, and you can look up the specific HP for your car as measured at the wheels at http://www.knfilters.com

David Vespremi

June 10, 2006 at 9:04 pm
(40) carey says:

So I wonder how many of these people critical of the K&N’s level of filtration wait around 5 or 6K to change their oil because of an oil life gauge? So what if the K&N lets in a bit more microscopic particles, change your oil every 3K and they will be long gone before having any impact on your engine. Personally, I’ll use K&N, change my oil before it gets dirty, and have the K&N throttle response and a clean engine both.

June 11, 2006 at 3:22 pm
(41) Shon Barrett says:

With that 3000 mile oil change strategy I am sure that there would be no extra wear caused by the K&N. My Accord is not a perfomance machine so that is not my route, but I can see where you might use it if you wanted the most perfomance and you where changing you oil frequently. A quality oil filter will help as well. I have heard very good things about the mobil one line and also the bosch line. I have not heard many good things about fram.

June 12, 2006 at 1:06 am
(42) carey says:

The point being that K&N filters are for those who are attentive to their vehicle and are looking for added performance, not for those looking to avoid performing necessary maintenance.

June 24, 2006 at 11:13 pm
(43) Jake says:

I recently changed my filter and added one of these performance filters (Green Filter, not K&N). It’s hard to tell if the horsepower has improved, having added something new I sit there wanting to see a difference. It may feel bit stronger, but the difference isn’t much. However I can measure the difference at the pump. I’ve always kept track of my MPG and it has been pretty steady at 17 to 18 miles per gallon. I usually get about 280 or 290 miles out of my tank before the fuel light turns on. My first two tanks with the new filter produced 19 and 20 MPG. The former being mainly street driving and the latter being almost entirely on the highway. I was pretty pleased and surprised to make it to about 330 miles before my fuel light lit up. I’m vary happy about it so far. I’ve also switched back to 87 octane. About two years ago I started to hear a strange noise from the engine (like it was gasping) while driving up hills. The 89 took care of that. One tank so far with 87 and no noise, we see how that holds up.

I live in San Diego and we have some of the highest gas prices in the country ($3.15 is about the cheapest I can find right now). All in all, if things stand as they are I looking at saving about $6 $9 per fill up.

July 5, 2006 at 11:16 pm
(44) Michael says:

I have a 2003 4.6 auto, F150. Rather than spending all that money on a K&N and other things I simply drilled holes all over the outer surface of the air intake shroud and replaced the OEM filter with a thinner FRAM. It’s a pinch noisier now but improved power. I also removed the tail pipe and put a turn down on the end of the muffler to reduce the back pressure in the exhaust without increasing any noise. I also added Bosch +4 spark plugs for improved spark. The results… it went from 20.5 mpg to 24.7 mpg. (UK Gal) All it cost me was the plugs and the new air filter…. easy, cheap. Try it.

July 6, 2006 at 11:57 am
(45) Michael-2 says:

Oh.. and maybe I should say I’m not the “michael” above. I guess I should be Michael-2.

Another thing re K&N. I bought a FRAM air filter for a 2000 Taurus at CTC here. They also sell K&N and they have that nice little display with the ping-pong ball that floats in the air. I removed the K&N and stuck the FRAM filter on the hole…. and what do you know… the ball floated up in the air just like the K&N did. The K&N filter here is almost $100. The FRAM $3. I can change an awful lot of filters for $100.

There are numerous such products out there.

I have seen people spend $500 to $600 on an exhaust system to get 5hp more. I’ve seen people spend $200 for a new intake to get 2hp more. The claims of 15 to 20 more hp are, to put it bluntly a lie in the real world.

BSC sells a unit with software that connects to your OBDII port and your laptop. One of the features is a “Dyno” chart. The only thing is, you need to find a road not watched by police… because your running in the real world, not on a set of drums. With this kit you can check real world HP gains… that are no way what these manufacturers and their sales people claim. They just want the money out of your pocket.

That’s the bottom line.

July 6, 2006 at 12:21 pm
(46) Aaron Gold - Cars Guide says:

Just had this same conversation with the K&N guy. We have a Typhoon system here for testing. I was concerned that the 6 hp gain won’t really noticeable and questioned K&N as to whether running this intake on a 96 Accord station wagon was a fair test. But they sent over the dyno charts that show a power increase in the RPM ranges where the car merges and climbs steeper hills. 6 hp is the gain in peak wheel HP, but the charts are showing a 1 to 5 hp gain in the 3600 ro 4300 rpm range, where a 5 hp gain is 10 to 15 % of the power being produced. In theory, we should be able to feel the difference. We’ll find out — I’m not going to show Robin the dyno charts, we’ll just install the system and see if there’s a real-world benefit that she can actually feel.

September 5, 2006 at 4:08 pm
(47) Karl says:

Here is something I want to throw out there for comments. I have read of problems with dealers saying that products similar to K&N will void your warranty. This is due to small particles of oil coming off the filter and clogging or deteriorating the intake sensors. I don’t like to throw hearsay out there but has anyone else heard of this?

Also, as an FYI, I put a drop in K&N in a 1987 Reliant. There was no driver noticeable increase in HP and gas mileage dropped 1 to 1.5 MPG.

If anyone wants to know about the Tornado Air Management System look here, http://autorepair.about.com/cs/productreviews/fr/aafpr052002.htm. Not very promising.

October 3, 2006 at 9:41 am
(48) billk says:

if I may.
If you ever have a question regarding physics, (which covers most human actions) I found the balance process works well. consider whatever you want to be a request from from MR. Universe. Mr universe simply places you request on the balance, notices the deflection and promptly requests payment. the payment is in direct relation to the deflection. Cash is not accepted.
You get nothing with out giving up something. Is the universal law.
IE on the race course everyone is in line for Less time. MR universe requires a payment in power or speed no escape, no checkout with out payment.
consider for a moment a modern turbo system and an air filter. The turbo boost is controlled at say 10psi boost. If the pressure drops, the bypass valve should close down some maintaining boost pressure. The turbo will be pulling harder but no matter, its a turbo, all that will happen is the air pressure behind the airfilter will decrease, increasing the pressure differential and increasing airflow. The compositon of the airfilter material is of no consiquence to MR Universe. Ok, airflow restriction=pressure which is a form of power or energy, pressure builds, (time lag) giving up time. airflow increases, all is back in balance total volume of airflow is maintained with only a momentary time trade which translates to a slight increase in turbo lag as its called.
I hope this helps

October 11, 2006 at 3:19 am
(49) mark says:

David Vespremi
K&N Brand Marketing Director should be ashamed of himself.

True, the KN filter is great for us racers that are able to re-use the filter in extreme environments at the track. However, there is NO gains in fuel ecomony, in fact, a dirty filter will save gas. (because you have less power to the rear wheels when your air filter is dirty) less power, less fuel burned. during cuise, the EPA and KandN are missing one major point, fuel economy depends on pressure drop across the throttle plate. the intake doesnt care if the throttle is closed or there is socks in your intake.

I recently did a test for some skeptics where i put a diaper in my air box. result was that i actually got better gas mileage during cruise!

an air filter have no more effect on gas mileage than the cost of gas will.

Dave, we love KN filters, but please, set the record straight. stop mismarketing your products. air filters dont give you better gas mileage!


December 26, 2006 at 10:16 pm
(50) Joe says:

I have been using K&N filters for years with out issue. I have put many, many many miles on an engine that is suseptable to dirt…..a rotary. I have at this point over 375,000 miles on this 1985 RX7 GSLSE. I put a K&N filter in it when it had about 50 miles on it and it has the same filter today. It gets cleaned with every oil change at 4,000 miles. It gets done by me. The facts as I see them are that most people that use a K&N will do there own maintence and cleaning. Also the amount of dirt that might not get caught by the K&N will be coming from someplace else like your fuel filter. How do you think fuel injectors get clogged or needle and seats get stuck. You have more dirt passing though your fuel system that your air intake. If your concerned with dirt in your combustion chamber look to your fuel system. The next big supplier inside your engine is your crankcase and oil. No matter what you use it all needs to changed. Oils main job other than lubrication is to suspend contaminates to be filtered and prevent damage and reduce engine temps. Some oils and type do better jobs than others but all will eventually break down and your oil filter is the limiting factor anyway. Ever wonder why race cars use dry sump systems and multiple filters. They caryy lots of oil to keep it cool and filter out the dirt.

The discussion of a K&N or paper element causing engine wear in my opinion is not reallt valid here. There are other areas of concern we should all thing about first. One is to just use some sort of air filter and service what ever one you use at least every other oil change or 8,0000 to 12,000 miles soon for those of us that belive in more frequent oil changes or drive harder or live in dirty areas like desert areas.


January 2, 2007 at 3:09 pm
(51) BL Bush says:

I had a K&N in my Yukon XL for several years. I started having “pinging” noises
and after much money replacing spark plugs etc, I found out the K&N oil particles caused my mass airflow sensor to fail. Now I use the Amsoil 25k filter to match thier 25k oil…no problems..

January 8, 2007 at 4:20 pm
(52) don says:

Funny that DV never claims that K&N filters better, isnt that the real point here?? He just mentions the “three legged stool” .

So better airflow looks to have less efficient filtration even in his statments.

January 12, 2007 at 4:30 pm
(53) Tom says:

A couple of thoughts …
On High performance cars from the factory — don’t you think it’s strange that when the manufacturers show their cars at SEMA and other industry shows they do use K&N air filters … perhaps the cost thing carries a little weight. The primary reason I see for a manufaturer not to use a product like a K&N is two fold — profit and driving conditions. They set service intervals based on average driving conditions and they never know if someone is going to be driving down dirt roads and filthy conditions on a daily basis or freshly swept highways. With spark plugs their environment is fairly controlled.

On filtration — I use a K&N air filter on my airplane. At each oil change the oil is analysed by a lab. The particulates and sillicats both decreased when I started using a K&N filter. My life is at stake here and that simple fact makes me a believer.

On mass air flow meters — The dealer tried telling my father that his K&N air intake fouled his mass air flow meter. When he took it to another dealer for a second opinion they found that his fuel pump was bad (there was nothing wrong with the mass air meter). The codes set in todays vehicles indicate a range of possible problems. I don’t know of one dealer that has a mass air meter test bench. Those idiots see a code and start ringing up the cash register. If replacing the mass air meter doesn’t fix the problem they’ll tell you that while investigating the problem they “also” found that your fuel pump was bad and the price to replace both was $1300. Thank you for stopping by. Next time bring your own lube.

January 18, 2007 at 5:37 pm
(54) chuck mrocco says:

My company Challenger aviation makes air filters for all piston powered aircraft using K&N Filter media.During hundreds of flight test hours in varous weather condition we consitanly saw inprovments 5%to7% in speed and .5 to 1.0 gallions per hour reduction in fuel burn. These are facts in the real world of avaition.As tom said, with our life on the line every time we fly,we monitor our engines much more than any of you experts.

January 25, 2007 at 9:23 pm

From a different perspective. After 25 years of racing and riding motorcycles in the desert or woods – where you’re constantly enveloped in clouds of dust so thick you sometimes can’t see out of them, I safely tell you that K&N filters do a great job of stopping the dirt – theory apart from everything else. Most everyone I knew used a K&N, and no one in all those years had to rebuild or deal with engines based on wear or dirt damage. Just my 2 cents. thanks all.

February 11, 2007 at 11:11 am
(56) Mark says:

Well is there any increase noticed in mpg with the k&n filter compared to the stock filter?

February 15, 2007 at 1:36 pm
(57) Jim says:

Try attaching the conical K&N filter directly or as close to the MAF sensor as possible. The difference in temperature will only exist while the car is not moving and will quickly return to the outside temp when it starts to move again. Plus you will be sucking air through a shorter straw and therefore getting more air. And, you will be using the high pressure area that exists near the firewall. Long polished and colored tubes look cool but only reduce efficiency. Try it – you’ll like it!

March 15, 2007 at 1:28 am
(58) otis says:

Aaron: Hellooooo??? Are you going to finish what you started???

Your first mistake is in asking or relying on K&N to supply dyno and other performance data. If you want objectivity you will only get it from parties that don’t have a financial stake in the matter. By the same token, you will have a tough time getting objective feedback from consumers as many of them will want to believe their choice is right and 99.9% of them won’t have any data worth a crap to back them up.

Do proper A-B-A testing in controlled conditions… or don’t waste everyone’s time.

March 15, 2007 at 1:47 am
(59) otis says:

Me again- I recalled reading a filter comparison in a car magazine years ago and sure enough, a quick web search revealed it to be available on the net. The good folks at Hot Rod Magazine did the dyno work that is too expensive and time consuming for most of us to undertake. http://www.hotrod.com/techarticles/70738/index.html

It appears they did a proper, valid test and the conclusion was that there is no functional difference in horsepower production between filters. I know you were looking for fuel economy data here but if the power production is for all practical purposes identical why wouldn’t the fuel efficiency be as well?

March 15, 2007 at 12:31 pm
(60) Aaron Gold - Cars Guide says:

Hey Otis —

I started doing fuel economy testing — but I just don’t have the facilities to create identical circumstances for different types of filters. I can control speeds, weight of car, etc., but can’t control things like traffic and the weather. K&N’s primary claim is that their filter will stay cleaner longer than a paper filter. Still haven’t put enough miles on the car to see.

March 15, 2007 at 10:44 pm
(61) otis says:

Apologies, I was a bit harsh with my first comment.

I saw this is coming up on a year now and thought it might have fallen off the radar. But if the test here is to road test the 50,000 mile claim, we might have to give this project 10 years.

Of course my conditions might be better than that of the average bear, but I had 80,000 miles and 10 years on the factory paper element in my ’94 F150 before I changed it… simply out of guilt (factory battery still in there)! So how do we quantify, by putting 50 or 80k miles on this Honda, if it’s better or not?

March 15, 2007 at 10:51 pm
(62) cars says:

Wait another 10k or so, then clean the K&N. If the car doesn’t feel any faster, I know it’s working! :)

March 15, 2007 at 10:52 pm
(63) otis says:

King of afterthoughts again!

One could test the fuel economy claims by- as mentioned- A-B-A. Now, environmental variables are such that running one tank through with filter A, second tank with B, third with A won’t cut it. But over the course of a year I would think enough data could be gathered so that a trend could be identified.

March 22, 2007 at 12:27 am
(64) ds says:

yes, i was wondering. I’m going to be changing my air filter pretty soon, getting a cone shaped one. I was wondering if i just got the cone at the end and not anything else would it still improve my performance?

…or could i just got the cone shaped air filter and the pipe to go behind it rather than the plastic in the car? does it matter about wats holding it up? or is it just looks?

April 3, 2007 at 11:03 am
(65) Akeem says:

Hi everyone I been reading both side of the story and decided to share mine. I had a K&N short ram filter installed on my 2006 toyota corolla. sounded nice, and had a good pickup after 3000 rpm. however, the engine light came on. I took it to a Toyota dealership, where they uninstalled and reinstall the intake tube. the engine light came on b/c the oil from the filter was clogging the MAF sensor. so they cleaned everything and only charged me for the diagnostic. I took a long road trip (approx. 600miles), and noticed that the Corolla had a hard time climbing from 70-90, whereas before the K&N intake tube, climbed with ease. The engine light came on again. AGAIN toyota told me the MAF sensor was clogged, and the intake was pushing in too much air making a (lean?) mixture. They reinstalled the stock intake for FREE and the engine light never came back on again. I replaced the dirty OEM filter with a FRAM filter, and it runs fine. Noticed I stressed the fact that Toyota was not trying to make money off the fact that I had an aftermarket intake tube. In fact, Toyota makes performance filters and intake tubes for select models.

April 8, 2007 at 1:05 am
(66) lc says:

A thought that not directly related to air filter. Most luxury cars (BMW, Lexus, Benz, Audi, etc) nowadays offer free oil change for as long as the car is under their 40-50k warranty. But then they say the car needs oil change every 15k miles. So that’s only 3-4 times they would do it for free. I think it make sense for them to raise the oil chance interval period to reduce cost of free oil change, and perhaps free loaner car that they have to give to customers.

As for those same manufacturers who also sell lower end cars like Honda or Toyota, they would tell you their 15k interval recommendation is for normal driving condition and for our city drivings, with lots of stops and go’s, it’s considered severe condition. They would automatically change the oil anyway (and charge you for it) everytime most people bring in their cars for service, when the cars preprogrammed service light would come on every few thousand miles.

Regarding the filter, I bought one for my car about 40k ago, and I think I should check it soon. But do I really feel the different then and now? I just don’t think anyone can tell a difference between a few HPs driving a car. And figuring out a few miles/gallon difference from day to day driving is just impossible. Even if one drives the same route everyday, there are so many variables: weather, traffics, number of red stops, speed, braking and who knows what else.

So, I bought it because it costs less than three time the amount I would have to pay for a paper filter but think it should last me more than that. I usually change my paper filter at every other oil change (about 10k). So, I am not loosing money, but thought why not give it a try. My car is at 120k and I don’t plan to drive it till 200k. Another 20k or so and I think I will have many other problems to worry about before my engine quits. It’s still running quiet and give me enough power and I think the synthetic oil/oil filter I choose to use make the biggest difference, and any type of filters I have used hasn’t done big enough damage, if any.

May 1, 2007 at 5:26 am
(67) John says:

I have a K&N type air filter for 9 years in my 1998 Grande Cherokee Jeep with a self built air induction system. Box has been removed. A clean air filter will give me better gas milage because more air is getting to the engine. .5 to 1mpg. With the K&N I can clean it any time I want. Planned trips, the filter gets washed and very lightly oiled. When cleaned, I can feel a difference. Since the filter is not in a box I can see easily when it is dirty. The cost was about $45. At $5.00 a pop for paper filter (123,000 miles)I have saved about 15 dollars. If I guess how many times I have cleaned the filter at $5 a pop because the filter was dirty or I was going on a trip, it would be more then a $100. It only takes 10 min to clean the filter.

The wife car fits more of the argument going on here. It is in an air box, Hardly gets dirty or checked. MPG I dout it. Performance may be a 2-3 horse. Worry free and I do not ever have to by another air filter for the life of the car.
If in the air box, personal preference. Both K&N or paper are fine. If an Air induction system, K&N type air filter all the way.
On the K&N ping pong testers, make sure that the back door is open when testing air flow. Door closed both filters raise the Ping Pong to the hhighest hight. Open the back door to let more air in and the paer drops the ping pong half way down the tube. K&N still keeps the ping pong at the top. Fans have remained constant. My .05 cents

May 14, 2007 at 3:01 am
(68) otis says:

John, pardon my French, but you are full of it. The throttle plate restricts airflow to the engine at your command, and unless it is at wide open throttle and/or the filter is darn near completely plugged, the filter isn’t much of a restriction. And even if it is somewhat of a restriction, the fuel injection system corrects the mixture richness for that.

It appears answers to the orginal question posed will not be forthcoming here. So long and good luck!

May 14, 2007 at 8:10 am
(69) Imp says:

Quick question/comments is anyone is still reading at home…

Many modern OBD2 fuel injected cars have sensors that are in a loop that tell the engine to add or pull timing, spark, fuel… all based on air-flow at the air-flow meter.

More air means the need for more gas so the engine doesn’t become rich which means: mo powa! Here’s where most High-Perf filters come into play. No doubt about it. The only way to add power through an air filter is to allow more air across the AF Meter.

This question came up on another forum that I frequent and on a quick google search, this site/blog came up re: ful ECONOMY.

It may sound kind of simplistic, but…
If you ran a restrictor on your engine, and got less air flow, the Air Flow sensor would record less air, the onboard electronics would sense that and decrease the amt of gas being added(causing a lean condition…. I understand that).

I (and others) contend that a clogged air filter will give you more gas milage as the system does it’s magic and only adds the amount of gas needed for the air that is coming in. It’s still a pump. THe computer system will adjust to make the fuel etc match.

Yes, of course you’ll lose some performance. We all read that 5-15-50K whatever for replacement of an air filter. Are there any studies anywhere that show the maximum a filter can be clogged before the computers can’t pull anything more because there’s just too LITTLE airflow being sensed by the AF Meter and you start to get detonation?

I (and some other like minded car-geeks) think that there will be a certain point, if the goal is to INCREASE fuel economy, that the air filter would be the way to go… up to the point where it’s detrimental to the car from too much blockage.

Thoughts? Again, this only applies to cars that use OBD with any kind of airflow sensor to control the amount of fuel being added.

Anyone know of any studies out there that have done the testing on ‘how clogged is “too” clogged’?

May 14, 2007 at 8:19 am
(70) Imp says:

OK, so I just re-read the thread and David said: “Department of Energy Report, a clogged air filter can negatively impact fuel economy by up to 10% and that there is a relatively high number of vehicles on the road using paper filters past a point in which fuel mileage is likely being impacted.”

David, if you’re reading this, do you have a link to the Dept of Energy report referenced above?

(Sorry I missed it the 1st time).

May 14, 2007 at 9:06 am
(71) Bill Hoff says:

use your K&N and then wip down the inside of the filter housing or induction tube and you will find lots of dirt. that speaks a lot more to me than statistics. We have lots of dirt in

May 14, 2007 at 11:07 am
(72) cars says:

Imp, et all –

Don’t forget that air flow is only *one* of the factors that the fuel injection system uses when deciding how much fuel to spray. There are several others, including throttle position. If the driver is flooring the pedal and the airflow isn’t coming, the electronics aren’t going to just shrug their shoulders and give up. Even a carburetor, which does meter fuel primarily based on airflow, basically tosses extra fuel in any time the accelerator pedal moves downward.

May 17, 2007 at 10:32 am
(73) Chris says:

I used the K&N cold air intake in a dodge ram with a V10 engine. Lost power, gas mileage and the engine began to ping.Took it off everything went back to normal. Good Luck.

May 21, 2007 at 2:51 pm
(74) Secret Sam says:

I am an engineer, specializing in air and fuel filters, at an American auto manufacturer and as a result must remain officially “off the record”. However, here is the last word on filtration elements (in laymon’s terms).

While we officially say we do not test aftermarket filters, the reality is that we do. We do so to understand the consequences of poor filtration. The filter element (the paper) used in our vehicles is the identical element used in the Ambrams M-1 tank and filters out 99.7% of all airborne particulates.

The purpose of the filter is NOT fuel economy or power, it is engine protection. This is the single most important reason for filtration. The OEM paper easily allows sufficient airflow to the engine required perform at specs. Airflow is a non-issue.

The aftermarket filter makers emphasize power and fuel economy as benefits, and filtration rates of up to 97%. However, none mention that the OEM filer they are replacing has a filtration rate of 99.7%. Basically, you are buying engine damage with all aftermarket filters. The only question is… is the damage sufficient to impact the vehicle to the degree that it is noticable.

As another writer mentioned, the computers monitor airflow and controls combustion, thus, the benefits of improved airflow (fuel economy) are negligible unless you also alter the computer control module. i.e. “chip” the motor. You can get improved fuel economy, combustionability, and power, as a trade off to engine wear or potential engine damage from higher combustion temperatures (and the resultant repair is NOT warrantable).

All test data supports the manufacturer’s interval for changing filters, excepting that local conditions warrant a more aggressive interval (see off road operating conditions, frequent towing, etc. etc). The reason for longer intervals with some aftermarket filters is that the dirt stopped by the OEM is NOT stopped by the aftermarket. Thus, it takes longer to stop up a filter with big holes! Doy!

While I have no date to support increased fuel economy with an aftermarket filter, I do have data that indicates a dirty filter can reduce fuel economy by about 10%. So its a matter of perspective. You can say “improves fuel economy by 10% when compared to a dirty filter” but not a new one.

Hope this is helpful.

June 5, 2007 at 3:01 am
(75) foobar says:

So… Any closure on this issue from the blog author?

FWIW, I have a K&N filter in my 97 Accord. I have no idea if it’s improved HP or saved fuel or cured the world from cancer, but I do know that I have saved a load of money from not buying paper filters over and over and over again. I’m not sure where people are buying FRAM air filters for $3; mine are a third of the price of the K&N, so I all needed to do to break even was to not buy two more paper filters. They also go on sale every now and then, so the savings can add up.

I don’t even care about any sort of specious claims made by K&N. According to every car manufacturer their car will make me the happiest person in the world as a result of the vehicle, and I have yet to see that happen.

I’m also surprised by the number of people confounded by the dealer maintenance argument. You bet your butt they schedule lots of maintenance. I can’t think of a single OEM part that doesn’t have a far superior aftermarket equivalent. The less frequent oil changes were as a result of people finally figuring out that, hey, 5K oil changes weren’t necessary. Any decent mechanic will tell you that these days.

June 8, 2007 at 12:24 am
(76) Bob says:

Wow…all over the place w/ this thread. I have ran paper, the “other guys” air intakes, K & N’s air intakes & filters. Paper less gas mileage. the “other guys” & K & N air intakes. K & N ‘OEM’ style filter. I have found no improvements. I dropped this filter in less than a week ago. I will say I wish I went w/ the intake system, but they didn’t make one for a Subaru Baja. At least, they don’t market for that car. It actually is the same intake as a Impreza.

June 11, 2007 at 6:26 pm
(77) Yossi says:

Excellent discussion going on here. I’m looking for a feature for my website Snails on Steroids. Anybody want to sum things up in an article. Will get full credit for the feature. We will also dyno 10 different air filters including K&N and King Dragon and paper filters. MPG / Filtration Rate / and HP increases will be taken into consideration. Let’s get this thing sorted out once and for all. http://www.snailsonsteroids.co.za – Just fill in the contact form and we will make a plan.

June 14, 2007 at 10:21 am
(78) Ockham,R says:

An independent research effort in 2005 looked at 5 top quality, brand-name, automotive air filters; concluding that while the air-flow of the K&N was excellent, it’s filtration ability the least of the lot. This is not suprising as K&N has engineered for the high-performance racing market – not the dusty streets and back-country. AC Delco and Baldwin make the best filters for engine protection.

July 6, 2007 at 12:26 am
(79) JohnB says:

Ok, I just purchased two K&N filters, one for my 2002 Civic and the other for 2004 Sienna. After reading these messages, I am a bit concerned. I wasn’t so interested in HP increase or mmpg improvement (although they would be really nice), I was attracted by longer maintenance period and overall $$ savings over 5+ years of the ownership.

That comment on Corolla also concerns me – would my Toyota also experience similar issue?

Has anyone on this blog used K&N on either Civics or Siennas?

July 7, 2007 at 3:03 am
(80) mark says:

Again, everyone talking about air filters effecting fuel ecomomy, should be ashamed of theirselves! as say in post 43 and otis and others say as well, the air filter is not part of the economy equation! the fuel metering system dictates the mixture. a clogged air filter, as i have shown, doesnt make a difference on fuel economy, in FACT, when fully clogged, your air filter will probably give you better fuel economy, as you cant get the air in, even at WOT, so you burn less gas, at a cost of HP, thats all! the wide open throttle switch has little or nothing to do with this, in fact, its a non issue, as modern EFI throttle position swiches are just that, switches. they dont do any feed back to the ECU in part throttle conditons, and thats what we are really talking about here with regards to fuel economy. HP gains, due to lack of restriction or greater restriction is an entirely different discussion. SHAME on anyone, especially from KN to even hint that their products can help with gas mileage efficiency! again, i stuffed a diaper in my air box, where i could barely reach 60mph on the hyway, almost full throttle, yet i got the exact same mileage on one leg of 200mile round trip as the the other leg with the air box fully functioning. why is that?? because the air filter condition does nothing to fuel economy!

July 7, 2007 at 3:11 am
(81) mark says:

secret sam,

we agree with almost everything you say, except the last paragraph. There is NO gains to be had by having a clean air filter or no air filter at all. the dirty it gets, probalby as you indicate, the better it filters (ie “smaller holes”) but if you tested 10% gains in better fuel economy, i say BS! you know it! Please elaborate on how this is remotely possible? the air and fuel metering system has no idea if the pressure drop across the intake is due to a partially closed throttle plate, or a clogged filter. what it does know, is relatively, how many molecules of air are moving into the engine, and it matches that with the appropriate amount of fuel. the ONLY way that fuel economy could be effected with a dirty filter, would be in a carburator equiped engine. then, i supposed a clogged filter could alter the mixture to the rich side, but that is not the point of the discussion here.

July 18, 2007 at 10:03 am
(82) Gerard says:

Is there anyone on this board that has actually worked on a motor?? Good grief, go back to school. ANY TIME you decrease the flow resistance with heads, air intakes, etc. you are INCREASING the EFFICIENCY the car has at moving air. By increasing the air flow and efficiency rates you are also allowing the cylinders to more effectively scavenge the exhaust gases out of the combustion chamber. Depending on how extreme the change is this improves gas mileage and power and it has nothing to do with friggin chips!! Here’s a bit of logic for ya. If you think that less air flow will allow the computer to magically calibrate and then run less fuel run a dirty air filter and see what mpg it gets. P.S. having a K&N sticker doesn’t mean you get paid. I personally race and people put them on cuz they think they’re cool. The hotrod article link is bad.

July 18, 2007 at 1:44 pm
(83) Brian in Denver says:

This topic has been the most head racking to research. Most people I believe are lead to believe their investment works – That’s marketing! So they spit out their great reviews – which hampers research.
SUMMING it up – I believe that after market filters will save you money and with PROPER maintenance the dirt that does get through will not affect it. There is always the special case.

My question that I can’t seem to get a stable answer on is — Will fuel economy improve with a CUSTOM AIR INTAKE SYSTEM AND CUSTOM EXHAUST SYSTEM? It’s a decent investment and I really want to know if it’s worth it – besides hearing a loud roar when I floor it – which got me my DUI. Note – Don’t install an intake kit on a weekend and drive home that night drunk.

July 24, 2007 at 1:46 am
(84) mar says:

Gerald, I race and have build race engines. I know what i am talking about here, while i think you need to look up the definition of efficiency. the problem, is that folks like you tend to try and make sense of air flow, HP, efficicny with intuition. air flow dynamics of an engine are not that simple. you have to look at the bigger picture sometime to see what is REALLY happening. Ive already done the test with a 2000 BMW 328 by clogging the air filter with a rags! it was so clogged, i could barely accelerate to freeway speeds. HOWEVER, on a 200mile journey, i was able to reach 1mpg better gas mileage. WHY, because your engine doesnt know the difference between a clogged air fliter and a closed throttle body. its a pressure drop!!! plain and simple!!!

Yes, the mass flow sensor basically measures how many molecules are passing through it by a tempurature drop of the “hot wire”. (or voltage change by deflection of a AFM barn door, or voltage change of a intake MAP sensor )

these signals tell the computer how much fuel to provide the engine at any rpm based on how much air is moving through the engine. IN my case, mixture were kept constant, even though i could barely make 50hp total out of a car that is normally rated at 200hp!

People always mock what they dont understand.

air filters do not effect the efficiencies of engines. they dictate cleaning of the air passing through them, at a cost of some pressure drop across it. generally, there are trade offs, but KN does a great job of giving adaquate cleaning, with low air flow resistance. They do NOT effect gas mileage, no filter will effect gas mileage. anyone that claims that it will is lying and any company that says it is criminally misrepresenting their product!


July 24, 2007 at 1:56 am
(85) mark says:

Brian from denver,

No, air intake systems do nothing for fuel econmony. Think about it. if you have a clogged air filter, or a stock intake and then you add a intake tube, that is low restriction, what happens?
for a given throttle setting and cruising speed, if the air passes easier through the intake, THEN, you would have more molecules of air passing, for a given throttle setting. With me so far? good. Now, this means more power is going to be produced and your cruise setting would suddenly be changed to acceleration. you would then have to match the power setting by closing the throttle. (ie lifting off the gas slightly) whether the air is resticted at the filter, air box or throttle, the engine doesnt know. the word “Throttle” means “CHOKE”. the throttle is a variable choke. you want more air flow and power, push the gas down. the less air that flows for a given speed, the less fuel that will be used and the more the fuel economy will be increased. How well the fuel is burned is a function of engine internal designs ( timings, spark, air flow characteristics in the combustion chambers, etc). then, the other major factor is aero and rolling frictions.

exhausts can increase fuel economy, based on helping the combustion process and evacuation of the gasses. However generally, those gains are slight, due to the low mass flow rates at crusing speeds and the low power reqirements to keep vehicles at those speeds.


July 27, 2007 at 8:29 pm
(86) Kevin says:

wow, i gave up. I can’t read this anymore. I got about 3/4 pages but some of you need to learn your facts before you post your randomly made up facts. True K&N filters are used in Motorsports, but iv’e heard, not saying this is true in anyway that indy cars engines need to be remade after every race because they get so hot and actually warp. I know several people who have K&N and are very satisfied, but you won’t get much of a gain in horsepower and torque unless you get the intake kit. Bash whatever you want of what i just said, but majority is fact.

August 16, 2007 at 8:07 pm
(87) Jack says:

This guy actually RAN TESTS:
Bob the Oil Guy

He compared paper, oil, and foam air filters, including k/n

As with any engine design decision, like selecting an air filter, there are tradeoffs.

The amount filtered was inversely related to the volume of air flow. Makes sense to me: smaller holes -> catches more particles -> decreased air flow.

The inverse is true too: bigger holes -> catches fewer particles -> increased airflow

So there’s your tradeoff: cleaner engine OR more air, not both.

There are things that are counter-intuitive in this world… this one isn’t.

August 29, 2007 at 7:43 pm
(88) randy kubick says:

K&N air filters are pure marketing just like pet rocks. Less we forget, gas engines must run at an air-to-fuel ratio of roughly 14:1 (14lbs. air to 1lb. of fuel). Deviate from this ratio even slightly and your engine will let you know by overheating if too lean and high fuel consumption if to rich. Thus, for well over 100 years gas engines have used a throttle in the intake air stream to maintain the correct air to fuel ratio. So K&N may have a free flowing intake filter but it really is a mute point because after the air filter is a “butterfly” which throttles down (restricts) the amount of air entering engine. The only time a K&N filter would be any good would be at wide open throttle which also means more dirt for your piston rings. But don’t get me wrong, I like K&N air filters. I’m in the engine rebuilding business and these filters have brought me a lot of business. Of course my customers don’t much like them……any more.

September 1, 2007 at 10:07 pm
(89) mike says:

I would highly recomond the following, Forget about oiled filters. Forget about high flow filters. lets start thinking about extreme filtration and go with a 3 filter array not just one. The single filter that filters out allmost everything is too restrictive but 3 of them and you get the best of both worlds. I have a 350z and I had a buddy machine a 3 filter cold air instake system based on the secret weapon r intake tube system using extremely restrictive microfiber filters NOT HIGHFLOW. before when i changed my oil @ 2500 miles is was dark or black, now it looks just like it did when it came out of the bottle, alltho it took 3 oil changes to filter out all the bullshit that got in there from a single oiled k&n filter i used in the past, now I beleive to be legacy technology. I also suspect the oil filters are severly inefective. ( think service ) I am try to see if there is a market for a filter array based on what i have seen with my own eyes. What I cant beleive is why this has not been looked into b4. My conclusion is that the entire industry is in-bed with eachother so that hundreds of millions of dollars can be made off the severly inefficient air intake systems. filters, oil, gasoline, engine rebuilds ect…. Don’t beleive anything from anyone that works for a company or corporate entity, they are bound by there jobs to increase revenue, bottom line. see past the bs and you will be rewarded.

September 1, 2007 at 11:10 pm
(90) mike says:

again the topic is air filter get it guys FILTER the whole point of a filter is to do what ? durrr filter so the best filter is allways the one that FILTERS the best. are you getting the point f i l t e r spells filter. lol

September 1, 2007 at 11:23 pm
(91) mike says:

Mar hit the nail on the head. I would say forget single filterd systems. How about 2 extremely restrictive filters instead of just one. this way you get higher flow and better filtration. Looks like the new 350z’s have a dual air intake system but how about 4 filters , you see what i’m saying ? who wants to reply to this idea ? I know dual intakes have been around for a long time now but efficiency is becomming more important to people and oil and gas has gone up so much. so how about 4 highly restrictive air filters. lets see who else thinks this is a good idea

August 24, 2011 at 5:04 pm
(92) Harold says:

I like Mike’s idea of multiple “restrictive” filters. I have been thinking about this for my Jeep TJ. I had an Airraid (similar in concept to a K&N filter), but removed it & went back to the stock paper elelment system because I was skeptical of dust getting by the Airraid in the desert environment where I sometimes venture. The cleanable element when held up to the light seemed porous. I will say this: the Airraid system did let me carry a taller gear with my 5 spd up mountain grades. Therefore my engine was definitely making more torque. Another Jeep owner I spoke with experienced the same result with his after market intake filter. Getting back to Mike’s concept: don’t dirt track cars stack multiple air filters on their intakes?

September 5, 2007 at 8:03 am
(93) Mark Morgan says:

I have run three cars on K&N filters and have to say that the filtering/cleaning side of things is poor as it lets to many particles through to your MAFS/AFM. Also because it’s an oiled filter the oil causes the elements in your MAFS to gum up. In all cases I switched to Apexi (even on my Jaguar XK8. They are oil free filters and all independant tests I’ve seen show that they are the perfect balance between maximum HP and good filtration.



September 7, 2007 at 12:43 pm
(94) Wight13 says:

You keep claiming that clogging you air intake actually improves fuel economy but I call bullshit. You also say that you can barely accelerate to interstate speeds. Slower accelerations and lower speeds will increase your MPG dummy. Try driving your car at the same speeds and slow acceleration with an unclogged intake and then tell us what the fuel economy comparison is between a clogged intake vs a free flowing one.

October 2, 2007 at 12:01 am
(95) Grinder says:

I’ve been using K&N for years – both their drop-in replacements and FIPK intake systems.

What we’re forgetting here is you do what pleases you.

If putting a K&N in your vehicle gives you the illusion of extra mpg, or extra power, then good.

If it actually DOES give you extra mpg and more power, then good.

Just keep being happy and keep your oil changed regularly and all will be fine.

What I’m saying is, who gives a crap what anyone thinks, so long as YOU’RE happy with what you got.

October 17, 2007 at 7:37 am
(96) Rod Lawrence says:

Wished I’da found this website before I dropped my sixty bucks! Dropped my K&N into a 99 Chevy Express 1500 w/ a 5.0 Litre. Lost a .5 mpg. HP gain, maybe 1 or so (been running small blocks a lot of years, so my foot knows the difference!) Up side? The oil’s still clean after 2500 and it’s been drier than a popcorn fart here in MI. For certain going to tear down the intake sys. and look for oil residue and if there is, any body in the market for a used K&N? Thanx for input here CU

October 17, 2007 at 2:50 pm
(97) Karsten says:

OK, I bought a K&N filter recently. Haven’t put it into my ’07 freestyle yet. I was hoping for a little better mpg. After reading this forum I searched a little more and found the following site:


October 23, 2007 at 9:06 pm
(98) Jon says:

After reading through the comments I have a few observations.

1) – K&N does not claim a mpg benefit associated with the filters. They point out that results will vary. Some customers have noticed an increase (probably due to changing driving habits, conditions, other factors, coincidence, want to believe, etc.) K&N simply uses the testimonials and anecdotes of happy customers without making any direct claims. (sounds like good business to me) MPG is simply not a selling point for the filters.

2) – It would appear that K&N filters do not filter out quite as much as the standard paper filters. The question remains as to whether or not it is enough to make a difference during the typical lifespan of a passenger car engine. The knee jerk reaction is to say any dirt is too much dirt, but with other factors involved, that can’t really be said without direct testing of actual engine wear. After all, if changing your oil at 3000 miles is good, then why not change at 1000 miles? Wouldn’t there be 3x more dirt in the oil at 3000 miles? Should we change every 100 miles? Apparently, it doesn’t affect the life of the engine enough to warrant the extra work/cost. Something to do with diminishing returns I believe. The question is will using a standard filter help your engine last 10% longer, 1% longer, or .0001% longer? I don’t see any scientific test providing an answer.

3) – It seems as though K&N has two very different customer bases. Those who want performance gains (opt for the intake systems with proven HP increases) and those who want to simplify the scheduled maintenance on their car. I think that typically, the HP junkies are willing to accept some trade-offs (the prospect of more dirt getting through the filter) After all, speed demons make many other costly sacrifices in the name of fun (tires, clutches, traffic tickets, etc.)

While the “ease of maintenance” customers would probably not like the thought of potential added engine wear.

I like the idea of double filters for this group (those not interested in HP increases).

K&N – is it not possible to add a paper filter after the oil filter in the setup. If several of these paper filters were included with the oil filter purchase, you could still claim the long duration between filter cleanings/changing and the benefit of never having to buy another filter. With such a small fraction of particles making it past the first oil barrier, the paper filter should last a very long time. The filtration should be better than any paper filter on its own.

4) – Race vehicles should not be compared to passenger cars with regards to engine longevity. Someone correct me if I’m wrong, but getting a race engine to last 100,000 miles+ without any need to tear it apart is simply not a priority (probably not even a possibility). Engine rebuilds are a fact of life in racing no matter which filter is used.

5) – If you want better mileage, drive slower, accelerate slower, shift sooner, properly inflate your tires, etc.

6) – Opinions are like air filters, even when full of crap, they will often go unchanged.

November 4, 2007 at 4:00 am
(99) Thomas says:

Well having read through all the comments, I did some research for myself.
Paper filters better – period!
I put a K&N filter in my vehicle 3 days ago, It will be removed this week, and replaced with a new OEM filter!
Found this handy test on the web, its simple, but scientifically sound. http://www.bobistheoilguy.com/airfilter/airtest2.htm

November 4, 2007 at 4:04 am
(100) Thomas says:

…and here he tests the filtration, some interesting results, check out K&N’s contradictary comments in their email to him. lol


November 13, 2007 at 5:42 pm
(101) Roger Dodger says:

First of all, BobistheOilJerk is not to be trusted. He fudged his test of Lucas oil additive by adding it to gear oil, not crankcase oil. Then he ran it through what amounted to be a high-speed blender. And, then, Photochopped the results.

OK, here’s the deal with K&N filters. Car manufacturers do not put anything in their cars that is not going to make money for the replacement parts industry. Otherwise, we would have oil and oil filters that last 20,000 miles, so it is a bogus conclusion that car companies do not think K&N is better.

Next, K&N filters have a larger, usable surface area than stock paper filters. Why? Because the gaps between the folds in paper filters are more narrow than K&N. They have to be in order to have sufficient filtering capacity. Seems like the more folds, the better…but not so.

Yes, you can see holes in the K&N filter, but those holes are filled with oil. Just because you can see light through them does not mean they are empty. K&N does not make filters that let particles larger than one micron pass..and good luck to you if you can see a one micron hole with your naked eye. K&N filters turn black soon after they are installed wherever air has passed though it. What do you think that black represents? Soot? Burned oil? You will not see that on paper filters. So, what is K&N filters trapping that paper filters are not? Does it affect airflow across the K&N? Nope. Me thinks that K&N is trapping particulates that paper filters let go by.

Comparing new for new, STOCK K&N filters do exhibit a lower pressure drop across their surfaces at maximum air flow (WOT at redline) than do STOCK paper filters.
Aftermarket intakes are something else.

Comparing used to used, STOCK K&N filters exhibit an even lower pressure drop across their surfaces at maximum air flow (WOT at redline) than do STOCK paper filters.

Helps to have a manemometer, or some other measure of pressure differential to make that claim, and I do, and I have.

BUT..her’s the rub, a used K&N filter that has been cleaned and oiled properly WILL NEVER BE AS GOOD as either a new K&N OR a new paper filter.

Why, you might ask? The reason is because there are particulates that stay embedded within the K&N filter element despite your best efforts to clean them out.

Remember, though, that this advantage does not last for very long. Yet, if you must have the best flow for any go, then change your paper filter every 10k. Why not? You change your oil every 3k for more.

Cost? You are complaining about the direct cost of a K&N versus a paper filter? Let’s see. How many $15 paper filters would you have to buy after 100,000 miles of use? With K&N, you do not buy new filters.

BUT…like I said, a used K&N will not perform like a new paper filter. Yet, there are also superior paper filters, too.

AEM dry flow is one, and even Purolater has a high-output paper filter that is worth the extra cost (still half of a K&N) and will give you a flow rate very close to a new K&N.

Lastly, there is the hassle of cleaning K&N’s. It is literally an all-day affair: one hour spent for cleaning and oiling, and 10 hours for drying in between cleaning and oiling, and 12 hours after oiling.

Try putting oil on a wet K&N if you want a fast way to ruin it…so, yes, you do have to wait until it is bone dry before oiling. Also, you will not mess up your MAF if you be frugal but thorough with the oil, and let it dry,dry,dry before using it.

The choice is yours to make. Choose wisely, My Son.

November 16, 2007 at 9:09 am
(102) Mark says:

Hi thought I would add my comment, seeing as I’ve just install a K&N filter for my mazda 3 sport 2.0l 2006reg brought new, done about 8500miles on it and the oem filter hasn’t been replaced since getting it. First impression with the K&N filter is that my car felt and ran smoother then with the oem filter and have done couple of trips to town and home driving the same route and made notes of the mpg being report by the onboard computer, with the oem filter was roughly doing 26mpg and with the K&N filter got 29mpg, so for me I have gotten a better mpg from the filter and a better ride. :o )

November 25, 2007 at 8:44 am
(103) mike says:

You guys lol
1. stop with the emotional posting, that helps no one.
2. the whole reason there are filters in a car is to filter out dirt.
3. the best filter is allways going to be the one that filter out the most dirt.
4. re read line 3
5. again
6. i went with a 3 filter system and at 5 k miles my oil looks brand new. so I win.
7. the reset of the posts are pointless
8. whooz ur daddy. ahahahaha

November 27, 2007 at 2:10 am
(104) Geoff Tarnik says:

One fellow in this discussion claimed that the “revenue stream” theory is incorrect. Clueless individuals like that make America look bad. My advice to you: go back to school, read some books and then come back and theorize some more.

It is a fact of life that businesses concentrate on creating continuous revenue streams. The classic example would be the shaving razor, where Gillette is losing money on the razor unit, but making huge profits on cartridges.

Likewise, you blabbered that it is not true that the medical industry keeps schmoes like you sick so they can make money. Well, welcome to the real world. Better stop reading and go for a healthy dose of McDonald’s crap – keep your doctors rich and happy.

November 28, 2007 at 9:34 pm
(105) Bill says:

It has been almost 2 yearts – time for the original poster to pony up some results.

December 8, 2007 at 5:37 pm
(106) mark says:

Yes it is true, a clogged air filter will yeild better gas mileage because it is restricting the amount of air that can pass through it under full throttle conditions (or any throttle setting ) Look up the word, “Throttle” It means, CHOKE! the throttle’s job is to choke the car of air to give a desired power setting at any speed or acceleration rate. I have proved that on a long 200mile trip, i averaged 27mph with a totally clogged air filer. on the return trip i got just below this with a brand new KN filter.
why?? because the new filter allows for greater hp at any throttle setting, and a clogged air filter limits power. Power is directly related to mass flow throught the air filter.

Trust me, its the truth. anything you hear to the contrary on this topic is utter BS! I race automobiles competitively, and i can attest to the benefits of the KN filter on HP gains, even as small as they are. we saw 5hp gains from a stock paper filter on top of 400hp.

I have never changed the filter on my BMW since i bought it 7 years ago, until i did this test. its still getting the exact same 27mpg. and the same 27mpg if i suff the filter with socks, sand ,and dirt as we did for the test!


December 30, 2007 at 2:16 pm
(107) Jay says:


Just bought two K&N filters for my two vehicles (haven’t installed them yet).

The main idea being to save money overall. It’s hard not to conclude that they let more dirt through (even their marketing guy tacitly admits that) than an OEM paper.

If I want my engine to stay in excellent condition over it’s anticipated 200-300K life, then it doesn’t make sense to let more dirt in – that’ll obviously reduce it’s gas mileage later in it’s life.

More particulate = more wear. More wear = more gas blowing by the rings, into the oil. Poorer oil quality = more wear. And so on. Looser fitting rings = less available horsepower. Oil blowing into the combustion chamber = poorer ignition, fouled plugs, etc.

I’m not sure if saving a couple of bucks annually on an air filter will outweigh the poorer fuel mileage over the long haul; and possible engine rebuild

Damn! Can’t think this is going to reduce my total cost of ownership over the long haul.

Back to the drawing board.


January 7, 2008 at 1:33 am
(108) JimM says:

So after reading all this, who do I believe. I’ve used K&N filters in all my vehicles for years, and cleaned and re-oiled,and yes it’s a time consuming pita. I believed what it said on the box. Now, I don’t know. K&N, paper, even a dirty sock (not really dirty but looked good typing it that way), apparently they all work in different ways. The more research you do, the more varied answers you get. I think on my new car, I’ll put in a good quality paper filter and check the box for dirt after a couple thousand miles here in the Phoenix desert climate. I’ll check behind the K&N in my truck to compare.

January 10, 2008 at 1:06 pm
(109) mark says:

The bottomline is this:
the KN is cleanable, so it saves on replacement costs.
It also will allow more air to flow under WOT conditions. (more power) However, this could be at the cost of dirtier air, but i have doubts if that can effect engine live with the actual difference this would be vs a stock filter.

It in NO WAY helps with fuel economy. actually, it can only hurt, not help.


February 1, 2008 at 3:48 pm
(110) Steve says:

This thread must be a guiness book of records! Its been raging for years…

The ‘why dont manufacturers fit them’ question interests me, its true manufactures benefit from sale of replacement parts, but sometimes they push the boat out with special editions, where a car will get a special sports exhaust or something, they cant make much money from these specials, why doesent someone ask Toyota or Ford, or Saab etc why they dont fit these higher air flow cotton filters? By the way new Alfa Romeos are the best cars in the world, its been proved by scientists.

February 22, 2008 at 12:23 am
(111) Jody says:

I put a K&N filter in my truck and a K&N in my wifes car at the same time. The MAS had to be replaced in my wifes car and my fuel economy dropped 3mmpg in my truck. I had to clean my MAS and I got my mileage back. The mechanic told me it was due to the oil coming off the K&N and burning out the sensor, luckly the MAS in my truck just needed cleaning. These were OEM replacement filter style K&N’s. Pre-oiled from the factory. It was an expensive lesson.

To the guys thinking a clogged filter gives better economy??? Don’t you have to open the throotle up alot more to get any useable hp thus hurting econonmy, also the MAS isn’t the only senser in the circuit that dictates how much fuel is dumped, You have throttle position sensers as well, O2 sensers, IAT sensers, etc.. Your staement would hold true only if the MAS was the only sensor to dictate fuel consumption.

If you don’t have to open the throttle up as much to acheive the same amount of HP, you get more HP at lower rpm’s which in turn will provide better economy, sure you may get better economy at cruising speed, but you had to use twice the amount of fuel to reach cruising speed, Stop and go/city driving is where less restriction is going to shine the most and is where most of our driving is done anyway! If all you’re basing you theory/test on is cruising/hwy mileage, fine, but you need to figure/calculate how much fuel your using to get to the highway and to reach cruising speed!

I still use high performance filters, I just don’t use any that need oil to make them work! They will give you better economy in stop in go/city driving because you don’t have to open the throttle up as much to get up to speed!

You’re right, the ECU doesn’t know the diff, between a clogged filter and a clean one, but it does know how much the throttle is open, the more the throttle is open, the more fuel it’s going to dump!!!

March 9, 2008 at 2:23 am
(112) mark says:

Jody, sorry, that is incorrect. many folks talk about TPS (throttle position switches) but in actuality, for street cars, they are no more than limit switches. Idle and WOT (wide open throttle, or some proportion of full throttle) If they were true TPS’s, then you would be right. the added restriction due to a clogged filter would require a wider throttle setting, thus creating a higher fuel consumption setting. HOWEVER, if you are not driving a race car in ALMS compeition, you probably dont have one of these type systems.

Our cars. (ie street cars) dont have this type of open loop system, rather, our cars have a MAF, MAP, AFM or even carburetor, that pulls fuel based on its mass flow detection. So, in the end, my freeway AND traffic driving yeild the same MPG, in fact, it was better with the clogged filter all the way around. Why?? for the reasons i mentioned in several post earlier.


April 10, 2008 at 1:17 pm
(113) Andrew says:

well, the paper vs. k&n is debateable. i have a 1992 chevy cavalier that used to have a box, paper filter and air sensor in it until my friend took it all out before i bought it. before he took it out, it was getting between 30-32 mpg average. now with the k&n, and all the parts out, its getting 35-38 average. we did the testing for the averages both on full tanks of gas, and the k&n seemed to help alot. i dont know if its just the car was so old none of it worked, or maybe the better and open air flow helped it alot, but the k&n helped my gas mileage by about 3-4 miles more. but also remember, this is just the filter and not the full intake system.

April 20, 2008 at 10:51 pm
(114) tim says:

i have run regular paper filters k&n filters and k&n has helped mileage abit in my fuel injected and carbed vehicles. but right now i am more interested in the air intake system they offer since they are the only ones that build one for my 90 bronco but due to offroading on the weekends i plan on getting a fram filter to fit it. becuase it is a fact that cooler denser air does help mileage and performance versus a stock air inlet system

April 25, 2008 at 5:37 pm
(115) Edwin says:

You guys are forgetting what is probably the #1 reason most car makers avoid high flow air filters: The noise. From restrictive exhausts to quiter tires, great lengths are taken to reduce noise; and high flow intakes make alot of it. every time you floor it. For the average consumer, it can be quite disturbing.

April 27, 2008 at 3:30 pm
(116) Joseph says:

If people want a mpg gain with an air filer, I beleive they’re gonna ge sorely mistaken at the pump. A filter serves one purpose aand one purpose only: to clean the air going into an engine. What may help is a larger diameter intake duct. If a person switches out a 2″ diameter intake for a 3″, they’re allowing a greater amount of air to be avaliable for the engine to intake, do it wont have to ‘breathe’ as hard to get the required amount of air. Th only way to get more power AND better fuel economy is either to use a multiple filter intake system, or attatch a couple of oxygen tanks onto a truck and let just oxygen enter the intake. Sadly, the latter is heavy and expensive, and would be very complicated to set up.

I curently have a 1994 Chevrolet C/K pickup with a 5.7 litre stuffed under the hood. nIts also equipped with the Z71 off-road package, and as such, it is equiped with a pretty good intake system( for 1994). As of now i have the stock intake system and was considering upgrading with a K&N filter. Now, i believe it would be a better idea to supplement my paper filter with a K&N doing the initial filtering.

A MPG increase would be REALY nice, considering i get about 14 mpg as it is, and the fact that gas prices stink. An added couple of horses and torque wouldn’t be so bad either. but, ill try some set ups and see what results i am given. Until then, kep the suggestions pouring in!

May 8, 2008 at 9:40 pm
(117) Victor says:

Hi all, after reading quite a few of these updates, I had to skip to bottom, my eyes were crossing. I’ve tried K&N in a few of my cars, and can’t say I’ve ever been impressed. It has hurt the “off-the-line” in every car. That’s because the torque is adversly affected.

For example, my last three cars have been a 2004 Ford Explorer Sport Trac 4.0 litre V6, 2007 Ford Explorer Sport Trac 4.6 litre V8, and most recently, a 2008 Honda Accord V6 with 268 horses. None of them were the same off-the-line. I kept trying K&N because they were all different engines and I thought I’d find one that was positively affected. I like to get going from the lights and have the power I need when merging, or getting out of some idiots way. I’ve put the stock air filter back in in each car because it had a negative effect on the torque, and didn’t help the overall mpg in any car. It helps the highway, but hurts the city because letting in more air is great, but the computer has to mix more gas with it to keep the mixture right.

I was turned on to them years ago when a friend of mine had a K&N cold air intake on his Eclipse, and the horsepower was incredible. But after having a few myself, I realize that it wasn’t the filter increasing the horsepower, but everything else he changed. The intake, the chip, and the exhaust. To truely increase horsepower, the air has to get out just as fast, if not faster, then it’s coming in.

I understand why K&N doesn’t say their filters increase mpg, because generally, they don’t. I think that the reason why car manufacturers don’t use them is because of the negative affect on the torque. Off-the-line speed sells cars, it’s what everyone asks. What’s the 0-60 speed? Also, K&N’s take as to why car manufacturers don’t use them regarding the OEM filter sales. I don’t know about any of you, but I’ve never paid for a dealer filter, I’ve always gone to the local auto parts store for mine. That’s my two cents worth.

May 13, 2008 at 3:55 pm
(118) CARQUEST Teammate says:

Just testing to see if my security settings will allow me to post here.If so,I will come back and post a comment.Thanks

May 13, 2008 at 9:57 pm
(119) CARQUEST teammate says:

It appears I can.Good.Re:Performance improvements.An engine is basically an air pump.Any flow improvement in must be matched with flow improvement out,and vice versa, otherwise one will cancel out the other. Matching a high flow intake set-up to a free flowing exhaust will absolutely reap noticeable performance benefits.Re-mapping,or re-jetting will probably be necessary,however.
More on other points as time permits.

May 14, 2008 at 7:03 am
(120) Andrew says:

Regarding why OEMs don’t use the reusable filters, another thing to keep in mind is that it is a lot more work to wash the reusable one than simply replace it, making the paper filters much more convenient for the end user.

May 14, 2008 at 3:34 pm
(121) johmbodacious says:

I had just purchased to K&N filters, one for my 2002 Jeep Grand Cherokee with a 4.0L and the other for a 2008 Mercury Milan, I tried the filter on the Jeep, I deal in auto’s all day long, I travel everyday approx: 104 miles round trip. Up hills down hills stop and go traffic. Since the installation of this K&N filter I did see a small improvement in fuel economy, but I do travel at the posted speed limits, and even slower at times, with the price of fuel at a staggering $3.85 per gallon is just rediculous, so to comment on the K&N versus paper it’s all perception and opinions. you the driver must consider all the situations. conserve fuel period, maintain your service intervals, and save a little fuel for the next generation so that they can do their own investigating on which filter is better. Everyone is smart and intelligent and that’s what fuel’s the world.

May 15, 2008 at 11:19 am
(122) Matt says:

The only way to reduce fuel consumption is by reducing parasitic drag. This is caused by accessories like A/C, also by underinflated tires or drag by wheel bearings, a slipping clutch or in the case of a carbuerated car; poor mixture adjustment. Computer controlled cars are programmed to burn fuel at a 17 to 1 ratio of air to fuel. An air filter will not change this ratio. So you have 2 options to save fuel: lighten the load, or reduce drag.

May 18, 2008 at 7:58 am
(123) jason says:

it seems as though there is no more point in worrying about it so save your money on the apparent benefits and use it to pay off your bills or take yourself and the family on a trip to a remote area where there is no need for any more of this arguement. Companies just want your money so wise up.

May 23, 2008 at 11:07 am
(124) Air says:

I never knew I was so dirty. Thanks for the filter.

May 30, 2008 at 1:06 pm
(125) mark says:

Victor, andrew, Joseph,

Air filter DO NOT SAVE GAS and give better gas mileage!! PERIOD, you reasons and tests are bogus and make no sense. I gave the reasons in several posts above. PLEASE re-read them and try and understand the concepts. Yes, the engine is an air pump, but getting the air into the engine with less restriction helps only ONE FACET OF THE SYSTEM! WIDE OPEN THROTTLE!! a that point, the restrictions create pressure drops that can determine the power you have available. AT ANY OTHER TIME, at part throttle, and we are talking about cruise power settings, the THROTTLE IS THE MAIN RESTRICTION, as that is its JOB!!!!! the more restriction, the less air molecules you let through, the less gas is matched for that power setting (ie cruise on the highway). You can measure the power setting by vaccum levels in the intake. As i said, i can give you a 15hp power setting by clogging your intake with dirt, diapers, etc, and have you press the pedal to the floor, or you can have a clean air filter and the throttle plate almost closed. It doesnt matter. ITS ALL ABOUT how many molecules are let into the air pump, and NOT how “easy” it is for the air to enter the engine. making it hard, is called “choke” or “throttle” and thats the Throttle’s job, to restrict air flow. the air filter has NOTHING to do with this, until the throttle is wide open.

This is why i was able to clog the filter almost entirely, and floor the car for 200miles and get better gas mileage than with a new filter!! WHY?? for the reasons ive mentioned. Keep in mind, this is true for ALL Fuel Injected production cars!

any questions???


July 8, 2008 at 11:35 pm
(126) Todd says:

I recently had a friend who improved MPG in his car and truck with K&N filter. I installed in my Avalance and immediately noticed a smoother running engine with more pick up. Felt like I was gliding. My 5 y/o son commented to me on the smoothness even before I did. I haven’t had it on the hiway yet with my camper but am excited to try. Maybe my paper filter was just dirty but so far, worth the 45 bucks for me.

July 16, 2008 at 12:53 am
(127) Jimbo says:

I installed a K&N drop-in filter on my 1996 jeep GC. I drive a lot on the freeway, and before installing the filter i had a consistent 18-19 mpg per tank from driving 70mph the whole time. After installing the filer, I am now getting a consistent 21-22 mpg instead. From others who have installed the filter, I have not heard of the increased amount of dirt particles actually causing any real harm. I’m driving about 5,000 miles this summer alone, so it will pay itself off…eventually

July 18, 2008 at 4:46 am
(128) Rick says:

Are you referring to drop in panel air filters or aftermarket air intakes? A cotton vs. paper drop in panel filter you will normally find no difference. So the only reason to buy one is if you into recycling. Now an aftermarket air intake is different. If the oem air intake was restrictive and you replace it with a less restrictive one you will see a hp and mpg increase. If the oem was not vary restrictive than you just wasted your time and money on nothing. On my 2003 Elantra the oem system had 11 count that 11 90 degree bends in it. So I built my own aftermarket shortram that only has one 90 degree bend. I ended up with a 2.5 mpg increase 29 to 31.5mpg. I can’t say anything for hp increase, but I do get a faster throttle response vs. the old oem system.

July 18, 2008 at 10:35 pm
(129) Dan says:

I see one problem with the theory on the K&N link claiming better fuel mileage due to the engine breathing better. When you increase the air flow, the computer, using readings from the MAP and other sensors , will adjust the fuel rate to reflect the air increase. More air usually means more fuel, or else you would be running the engine more lean, and possible damaging the engine. I could be wrong though.

July 18, 2008 at 11:04 pm
(130) mark says:


You are absolutely right.

The previous 2 posters are completly wrong. I dont care if they think they felt smoother acceleration, or better gas mileage, its just cant be a part of the result of an air filter change. ONLY (and let me say it again) ONLY, when you are Wide Open Throttle, will a clean air filter or dirty air filter alter fuel economy or max power output. at ANY TIME ELSE, the throttle plate provides all the restriction you would ever want. reduce the restriction (i.e. Push the Accellerator) and you increase power. Again, throttle means “choke”. thats its job. I currently run my intake air box with it stuffed with rags. my BMW barely makes 50hp now, and gets better gas mileage because it keeps me from ever getting near max power potential.

The only think the air filter can do, is give you a higher power output for a lesser or greater position on the gas pedal. This would be in extreme situations. you dont go on a highway and use 5% throttle setting and feel that your car is more responsive. That is just silly.

air filters have NOTHING to do with gas mileage. read my previous posts for the reason why.

May 18, 2011 at 12:21 pm
(131) wow says:

I know this is two years old, but after reading all your comments, I have to say. I won’t pay any attention to any of the comments you left on this anymore.

You run your BMW with rags blocking the intake box? Thats the stupidest thing I have ever heard in my life. No person with a high school education and some general car knowledge would think thats a good idea. Of course your mileage will increase doing that, your engine cant do its job. lets not forget what an enging is. Its a glorified air pump. All it does is pump air in and out, in and out.

rather then do they stupid thing (stuffing rags in your airbox. wow by the way, still cant believe someone would actually do something so stupid to a car) try not slamming down the pedal everytime you want to go. Your car can easily only produce 50 hp, dont open up the throttle ( Read: CHOKE! as you put on your comments.) very much. IF you put a stock car on a dyno and didnt accelerate rediculously fast, and had it going at a cruising speed of, I dunno, 40, the HP would be drasticly lower then the people that go on and slam the pedal down through the floor.

July 19, 2008 at 7:27 am
(132) rob says:

Just testing to see if my security settings will allow me to post here.If so,I will come back and post a comment.Thanks

July 27, 2008 at 12:19 am
(133) Sorry I'm an Engineer says:

I still find it amazing that people think magic works in the real world.
I was glad to see that several people accurately explained exactly why a clean or better air filter will not improve MPG. (Actually it can reduce it since it will effectively allow a more wide open throttle.) What I don’t understand is that this myth is still promoted by about every ‘Improve your gas mileage’ advice column. An example is the Uniroyal column on howstuffworks.com.

August 1, 2008 at 5:31 pm
(134) Rick says:

Under the Maintain Your Vehicle headline.

Breathe easy. Next time you get your oil changed, have the air filter checked as well.
Replacing a dirty air filter with a clean one can save up to 10 percent on fuel costs.

So less air flow means less MPG. So what are you people talking about? Clogging up you air intake and such.

August 1, 2008 at 5:48 pm
(135) Rick says:

I just have to add. The only way to get more air into an engine then it needs/wants is to turbo or supercharge it. The K&N filters and such are suppose to make it easier for the engine to get air. Do they make it easier, and does this mean more MPG? I don’t know that’s why I googled the idea and found this page full of idiots who claim to be engine experts who are touting a full load of bs.

August 17, 2008 at 6:28 pm
(136) Jose says:

thanx GOD i read this b4 buying a K&N. dude at the auto parts told me it was the best cuz i asked him. He was right bout synthetic oil, but not this lol. Anyways, the reason why k&n doesnt claim that it saves fuel is, BEACUSE IT DOESNT. they dont want any law suits. If it did saved gas they would post it on their front page, specially now with gas prices the way they are. Ima get a regular oil filter for now cuz it will keep my engine clean, until Im convinced there is a “magic” one out there haha. It doesnt make sense to put a filter that (your not even sure if it will save fuel) will save a tiny bit of fuel plus the hassel of cleaning it (filters are pretty cheap and NEW) to only find out that you had contaminents get in your engines and could eventually get fuked up or have other problems.

August 18, 2008 at 12:09 am
(137) Dan L. says:

The bottom line is that airflow into the manifold is controlled by the throttle plate. The total air resistance is the sum of the throttle plate, filter, and other intake components. Say the filter induces more air resistance for whatever reason keeping in mind that K&N filters provide less air resistance. In order to maintain speed, the driver will end up compensating automatically by stepping on the pedal more opening the throttle plate. Despite a high air resistance by the air filter, the resistance at the plate is reduced to compensate, making the net resistance the same, ALLOWING THE SAME AMOUNT OF AIR TO ENTER THE ENGINE. Likewise, if a performance filter was added, the operator would end up stepping on the pedal less increasing the resistance at the throttle plate ALLOWING THE SAME AMOUNT OF AIR TO ENTER THE ENGINE. In any case, the amount of fuel burned is a function of how much air enters the manifold. It is at this point that the sensors measure the pressure and temperature to calculate the right amount of fuel. So if the PCM systems work ideally, driving economically with the pedal down and a clogged filter is the same as driving econ with a K&N with the pedal further up. To phrase differently, the car uses air resistance to control the air entering the engine (necessary to prevent a lean burning air-fuel mixture). In the end, trying to obtain the perfect air:fuel ratio, the car will ideally use the right amount of fuel for the work (accelerating or cruising) being done. The position of the pedal does not exactly dictate fuel usage. It is more accurate attribute the net air resistance. Therefore, whether the operator needs to compensate for a clogged filter or not, the same amount of fuel will be used for a given work load (SUVs and trucks have relatively high workloads). The point where a clean/performance filter will make a difference is when the gas pedal is pegged to the floor. At this point, the user does not want to regulate air/fuel use, but as much air as possible. A better filter and or intake reduces net resistance allowing the engine to produce more power. less resistance:more air per time:more fuel per time:energy per time=more power. Senseless colons aside fuel economy is not improved theoretically at any point. But overall horsepower can be increased with performance parts; probably not a big deal for the typical commuter.

This is not to be all conclusive that the epa 10% estimate is wrong.

-for one thing, the engine computer also considers throttle plate position in its fuel calculation. If the filter was really bad (high resistance) the comp might consider the compensational throttle opening to be a demand for acceleration, thus spewing more fuel through the injectors than needed. Under this consideration, the factory computer probably functions most economically with clean OEM components, has a large margin for error, and is probably affected very little if performance intake parts are added
-The last bullet point is just one thing I thought of. I am sure I am not considering everything, just thought I’d throw in some of my reasoning

August 18, 2008 at 12:25 am
(138) Dan L. says:

“fuel economy is not improved theoretically at any point. But overall horsepower can be increased with performance parts”


fuel economy is not improved theoretically at any point. But overall horsepower can be increased with performance -INTAKE- parts

Example) On the exhaust end, less resistance will increase power and fuel economy.

September 11, 2008 at 12:36 am
(139) mark says:

Great. This group finally gets it.

Now all we need to do is get the EPA to fix their lies regarding ways to increase fuel economy.

September 14, 2008 at 2:38 pm
(140) Air Flow Engineering says:

Simply stated:

Never use a cotton gauze or foam filter in any application.

Restriction- In SAE J726/ISO 5011 lab testing, the cotton gauze filters become quite restrictive in a relatively short period of time. Once dust loading occurs, the restriction curve becomes very steep. Why is the oil necessary? In terms of efficiency and dust holding ability, they are generally poor. The amount of particulate that your engine ingests and moves along to sandblast the cylinder walls, combustion chamber and related parts is significant. Most gauze companies test using coarse rather than fine test dust. The numbers when tested with fine dust can be alarming.

Cotton gauze is not and was never intended to be, an engine air filter. It was used 40 years ago based on convenience and a lack of understanding regarding it’s performance. It has not changed since inception. Consider that 0-10 micron sized particles routinely do the damage. Open one of these gauze filters and take a look! If your not familiar with particle size, there are approx. 300,000 microns in a foot.

Consider the impact from the oil and cleaners. The cleaner is very harsh. Just read the warning label. Follow instructions! This is important. Gloves, respirator, etc. The cleaner is metasodium disilicate. It’s nasty.

The oil presents many concerns of it’s own. We have all heard about it’s impact on engine control system components such as MAF. There are now more serious concerns that apply to the management/emission systems.

How often are users actually cleaning and oiling these things? Cleaning, drying, oiling…you lose the car for the day, if, in fact, you actually perform this maintenance.

The main reason you see a massive amount of oiled gauze filters is due to the cost. These are very inexpensive to produce. The majority of the so-called performance companies simply buy the gauze media or they buy a gauze filter from an industrial producer. It’s very expensive and time consuming to produce a very high flow, highly efficient performance filter. They do exist! I remeber speaking to a gentleman years ago that told me a story about a new customer. He said that a gentleman had called and expressed an interest in industrial or medical grade gauze. When he asked what the intended purpose was, the man responded ” I’m making high performance engine air filters”. The gauze supplier was incredulous! Air filters? With this stuff? Oh well…his money was good.

And now here we are. Never use a cotton gauze or foam product as your engine air filter!

Cotton gauze is simply heavy marketing! Avoid it at all costs.

The new synthetics certainly offer somewhat better engine protection but they do so at the expense of restriction. These new “fibers” provide a restriction curve very similar to the OEM unit. The factory Corvette filter is a good example. It’s extremely expensive and does a reasonable job of filtration. However, the restriction levels are quite high. It certainly doesn’t resemble a “performance” filter in testing.

Search out the true performance filters if you intend to replace your existing unit. Never compromise high flow for engine protection.

September 15, 2008 at 3:38 am
(141) Richard says:

Has anyone noticed that about.com says you should buy an aftermarket filter to get better mpg?
3. Check your air filter
Also the theory behind this idea is simple. The less force your car uses to suck in air the more efficient it becomes, giving an increase of a few percent of overall mpg. All at a loss of filtration.
Which do you care more about a small boost in mpg are good filtration. I ask this because some people go 7,500 and 15,000 miles on an oil change. Money savings vs. engine life.

September 15, 2008 at 3:41 am
(142) mike says:

Has anyone noticed that about.com says you should buy an aftermarket filter to get better mpg?
3. Check your air filter
Also the theory behind this idea is simple. The less force your car uses to suck in air the more efficient it becomes, giving an increase of a few percent of overall mpg. All at a loss of filtration.
Which do you care more about a small boost in mpg are good filtration. I ask this because some people go 7,500 and 15,000 miles on an oil change. Money savings vs. engine life.

September 15, 2008 at 10:26 pm
(143) Engineered Air says:

We have worked with a company in the past that developed filtration and filter technology that consistently outpaced the others. Their specialty was sophisticated military systems. They began a performance line that eliminated the compromises that exist among many current filters. If you really want the best for your car in all measured categories, look them up. They’re in Forest Park, IL.

September 21, 2008 at 10:29 am
(144) and the result is.....????? says:

well does it increase fuel economy or not??? where is the follow-up article????

October 2, 2008 at 11:15 am
(145) Rick says:

If your really looking for mileage than there’s only one thing to do,build and install a hydrogen bottle!It really works and will cost you about 100.00-150.00 dollars,and about 4 hrs to build and install. I went from 20.3 highway to 50.91….17.3 city to 24.1 They require changeing the water in the bottle about every other week for best results 10 minutes.You can do your own research and build one or buy a book,I did both!

October 3, 2008 at 1:31 am
(146) sarcasm says:

Also the Flux Capacitor, you can’t forget that.

October 3, 2008 at 5:37 pm
(147) rich as heck says:

this fellow did a rather extensive study with pictures and test results
seems to point ou that all are filters are pretty close for power and dirt trapping


November 4, 2008 at 4:37 am
(148) Richard says:

I own a large shop and have had several opportunities to experience many of these “wonder” products. I can say for certain that I gain .5 mpg in a diesel truck with oiled cotton filters. In smaller cars the difference is hardly noticeable. Waste of money at that point.

November 23, 2008 at 2:47 pm
(149) Tom says:

i still find it funny that people claim a clogged air filter will produce better fuel economy than a clean one. with that being said when your filter becomes so clogged that you can barely drive, do you just scrape off as much dirt as you can and then shove it back in? theoretically it should be a “lifetime filter” for you. having worked in a mechanics shop for years mostly doing fluid and filtration changes, i can personally say that a clogged air filter will directly affect engine performance and mileage. maybe your car is different and maybe you like shoving diapers in your box.

get this: more air flow = more fuel needed. i’ll give you that. but lets say with a stock filter at 2000 rpm you have the same amount of air coming in as a k&n filter does at 1800 rpm. so the same amount of gas is being used at both rpm’s but one is revving lower, thus improving economy (dont jump all over me here i’m saying theoretically it should improve economy). and at wide open throttle, more air is getting into your engine than could be possible with a paper filter, so more fuel can enter as well = more power. its a no brainer.

with this being said, i am taking my k&n filter back tonight. i just got it yesterday and having done my research on other websites, and reading this WHOLE thread… I would rather sacrifice an mpg in a truck that gets 14 than have to rebuild my brand new engine down the road. going with a fram instead.

but a clogged filter will NOT improve mpg. try breathing through a paper air filter, then try breathing through a diaper.

November 30, 2008 at 11:33 pm
(150) matt says:

I have seen the dyno resukts for a car with a clean air filter compaired to one with a clean k&n and the k&n dose not add horse power to your top end. But it dose make the curve flatten out keeping you in your near your peak longer, and you shouldent use it on industrial equipment without a prefilter also available through k&n.

December 7, 2008 at 10:32 am
(151) Mark S says:

Replacing a stock air filter in a motorcycle or car with a K&N version will generally provide a boost in horsepower. My first experience was with my 1994 Harley Sportster 883. With stock filter it dynoed 39hp. With a K&N replacement it dynoed 44hp. After replacing the exhaust with straight throughs – the motorcycle dynoed almost 50hp.

My 1998 Z-28 Camaro generated 292 horsepower with the stock filter and 308 with the K&N replacement.

It’s my opinion that the size of particle passed by a K&N filter would be too small and not of a composition to be harmful to an engine. If you change your oil frequently – you don’t need to worry. Particulate matter of a type that could actually scratch the internals of an engine are not generally floating around in the air. If you live in an area where the air is rich with diamond or titanium dust – you should move as your life is in great jeopardy.

December 22, 2008 at 11:00 pm
(152) eric says:

well after reading this i will change my air filter (k&n)
what i have also noticed is that the k&N filter allows for more air to enter BUT!!! that’s because it has bigger holes that’s why more dirt along with more air go through

December 26, 2008 at 3:11 am
(153) this thread hurts my brain says:

I’m getting a paper filter with the martini attachment.

January 4, 2009 at 10:32 am
(154) Andy G says:

mark + dan.l have hit it right on the nose. So can someone tell me this. On my fiesta ST i have an exhaust restriction after my manifold, (ford purposely put this on for insurance purposes i believe to keep the hp @ 150. By adding whats called a FLEXIpipe, with a larger airflow primary, will this increase the MPG slightly and increase HP slightly, i beieve it should but need someone to clear it up for me, with all these MASSIVE brains on here :P . cheers!

January 24, 2009 at 1:27 pm
(155) mark says:

Tom and Rich,

You guys still dont get it. “Throttle” means “choke”!! This means that the throttle is the restriction. the more restriction, the less the engine revs will be. at max restriction, while keeping the engine barely running, equals IDLE! If you understand this, keep in mind that the Fuel managment system provides perfect mixture based on air flow meetering, and O2sensor information. IF i clog the air filter with a diaper, the car will have no power, and may need 1/2 throttle just to go 55mph, but your gas mileage will be the same. Rich, this is because the clogged air filter is now creating the restriction that the throttle plate doesnt have to. the end result is a power level, (cruise at 55mph for example),and fuel flow rate that would be equal with or with out the clogged air fliter.
In the end, air filters have NO bearing on fuel economy. The EPA is giving us BUM advice and it is a crime! In fact, the world could save millions of gallons of gas, if everyone would just let their filters get diry! As long as the dirt doesnt enter the engine, there is no issues, but a loss of power!
If you make more power, you make more Gas. Pretty simple stuff!

January 24, 2009 at 1:29 pm
(156) mark says:

Andy, yes you could get more power and better fuel economy if you exhaust system is providing restriction and you relieve it by the “flex pipe”.

January 29, 2009 at 2:48 pm
(157) Ktbrooks says:

I have a ’04 jeep grand with low low miles that I just put a K&N cold air intake on. It was normal for about two days, now it makes a loud air noise in the mornings (sucking) when it is cold. It also has a vibration/ratteling sound on aceleration that once warm lessons, and comes and goes. I am pretty sure it is the intake, and I will be taking it back off to see. Any other ideas???????

January 29, 2009 at 3:00 pm
(158) ktbrooks says:

Also its coming from the side the intake is on and DOES not sound like it is engine related. That’s why I am attributing it to the filter…

January 29, 2009 at 3:00 pm
(159) ktbrooks says:

Also its coming from the side the intake is on and DOES not sound like it is engine related. That’s why I am attributing it to the filter…

May 1, 2009 at 5:57 pm
(160) rob says:

Ive used K&N filters to try and improve mileage as well as a lot of other gimmicks to name a few acetone, MPG caps, Lucas oil&gas treatment, other oil treatments, synthetic oil(bad idea on older cars causes oil leaks), and there’s another one I’m about to try that a friend told me works.

Most results where inconclusive unless there is a sustained significant improved or worse gas mileage over several tank fulls it could be just one of the fluke mileage reading you get about every so many tank fulls. Only true way to tell is the actual mileage over several tanks full. I usually test for 3-5 tank fulls.

Something new I’m trying comes right down to the station, sticking with one station chain using any locations convenient keep track of dates, mileage chain and location. I have noticed about a 5-7% increase in one of the two chains I’ve tested and, another 5-7% on a specific chain location.

I’ve been testing these two gas station chains for over a year, and have kept accurate records making sure warm/cold weather testing is close to equal.

I wont mention the chains Ive tested because It may come down to the supplier and not the chain itself. Results likely vary from city state or region so chances are what chain that’s best here wont be best elsewhere, and I’ve only tested two.

May 1, 2009 at 6:49 pm
(161) Mike says:

So many arm chair engineers……… Bottom line-


K@ N filters work. Period.

May 4, 2009 at 4:58 pm
(162) scooterdave says:

My 07 Ford Focus manual says the air filter is not replaceable and is good for the life of the vehicle…..how can that be?

May 17, 2009 at 4:59 am
(163) Keith Lewis says:

This is not a scientific test on a K&N filter trial on a Citroen C1 but here goes.

Fit a new K&N filter purchased on Ebay for £38.
Fill tank with 95 UL
Normal driving until the low fuel light flashes.
Mileage 385.

This was repeated for 2 more tank fills.
Mileage about the same.

No noticeable performance improvement.

Purchase new paper filter from Halfords £12.

Same test – same forecourt.

Mileage 415 average.

May 17, 2009 at 4:16 pm
(164) rob says:

Mike bottom line is owners of vehicles don’t have a lab to test their mileage they use real world conditions emphasis on the REAL part.

Which data is more important to smart consumers mileage in a lab or actual mileage in everyday driving.

Speaking for myself I drive in traffic on roads and not with my vehicle hooked up to machines in a lab.

One thing Ive noticed lab tests about mileage they are very consistent that is consistently wrong Ive never owned a vehicle that got the mileage the EPA said it would with the exception of one which was factory built but not standard so accurate(now that’s funny accurate)EPA testing didn’t exist.

Keith no offense but your data proves nothing without figuring actual MPG(KPL KPG)mileage traveled/ gallons = MPG and where the miles where driven highway, urban, suburban, city inner city. After you drove 385 miles average how many average gallons did it take to fill tank ETC. Best way to get an accurate average MPG of several tanks is divide total MILES by total GALLONS used

May 17, 2009 at 9:07 pm
(165) MARK says:

Wow Can’t believe I read the Whole Thing. Just wondering about the best filter to put in my car. The usual paper filter will be the way for me. It’s cheaper and less time consuming to read about. Although the comment about dry air in Mi. (drier than a popcorn fart)did give me the extra hp and mpg to finish reading.

May 24, 2009 at 10:23 pm
(166) kingston says:

I can’t say I read every post, just all of the longer ones, but wow, this is one of those subjects that makes people really MAD. It’s like Fram oil filters, people read something bad, make the decision not to use it, and then get angry at anybody else who doesn’t share their opinions. I personally use a K&N in both my truck and motorcycle, and plan on keeping it in both. Before the K&N I changed the air filters on both every year. I paid a total of $80 for the 2 filters, so as long as I use them for more than 4 years I’ll be saving money, along with saving the resources needed to make the standard filters I would have bought. I generally change my oil using the “severe” standard, which is much sooner than I probably need, so I’m really not too worried about dirt or hurting my engine. If you don’t like it fine, but its my decision so don’t tell me not to use it, ok?

June 12, 2009 at 1:36 pm
(167) L505 says:

The reason K and N filters offer more mileage in certain conditions is probably because they let more dirt in, and some of this dirt is burned in the engine which adds a bit of free fuel to the car.

Does anyone know of something called snake oil? I saw it the other day and was going to rub it on my neck. Is it safe?

June 12, 2009 at 1:39 pm
(168) L505 says:

Aaron is really happy he got some free toys from the company so his cute little upbeat attitude (before any testing was even done) means he is biased. You are doing “bum tests” on what is “felt” in the car, and you want people take you seriously? I think not. Imagine a scientist feeling one day that gravity seemed “faster” so the laws of physics would change according to his bum condition.

June 28, 2009 at 3:38 pm
(169) Mondo says:

Trust me when I say this. K&N filters do increase horsepower but you will lose torque. They do not filter as well as factory paper replacements. I have test them at least a dozen times. You will get 3 horsepower at best on a stock V8, 2 horses for a V6 and only 1hp on a inline 4. Is it worth losing midrange power for a few horsepower at redline? Your choice pay $15 for paper or $40 for oiled gauge. No gas mileage increases were ever reported by my customers. All it is a sales gimmick. Don’t forget to pay $15 for the cleaning kit too.

July 12, 2009 at 12:27 pm
(170) WMX says:

Mike was right. MPG on clogged air filter will be the same as a new air filter on modern cars, though old cars will be negatively affected at 10-15%.

See http://www.fueleconomy.gov/feg/pdfs/Air_Filter_Effects_02_26_2009.pdf

August 2, 2009 at 11:44 am
(171) carrotsmit says:

i have a mazda 121 1.3i GLX and replaced my filter box and filter with a simota racing cone filter and my car has lost its power.

must i now design a box that will channel air from the front of the car t0 the box where i will have my cone filter or what? someone help me please.

August 6, 2009 at 4:01 pm
(172) Emile says:

I have spent a long time reading this thread and all I can say is wow! Very informative and a lot of different opinions. I just have to share my own opinion. I think K&N make some awesome performance products. I soooo personally was about to purchse the K&N, but I have decided against. My main reason? The oil and the method of cleaning where you can ruin the filter or your engine if you are not careful. So, in my search for a high performance and better performing air filter, I think I will settle with the Amsoil. Why? Because it is new technology and they claim to guarantee it for 4 years or 100,000 miles. It requires cleaning too! But guess what? I am happy you do not have to buy anything. That makes sense to me. Check this link and let me know what you think about the comparism to the other filters.  www.amsoil.com/StoreFront/eaa.aspx. I hope this helps.

August 30, 2009 at 5:46 am
(173) impee says:

my my, I have never seen so many postings regarding 1 topic in my life!

A couple of points that I noticed while reading most of the postings is that:

1) Many people seem to be hung on mileage improvement and disputed this throughout, trying to prove K&N wrong for their statements and further proving each other wrong. What I personally and logically believe is that K&Ns statement should not to be taken literally. In simple terms a filter that can stay cleaner longer (i.e. still provides air flow) is always going to give better fuel economy…so that is that! A clogged one is bad in every way!

2) Having a K&N air filter is seen by me as more of a convenience over a conventional air filter, also performance wise too. Buy it once and then you are sorted. Never need to go to the shop to buy a new one again…simply order the cleaning kit and use that over the years. This also allows you to clean the filter whenever you want, i.e. before a very long distance trip, etc.

3) Lastly, how many people keep a car it’s entire life? Even if you do, and change the oil atleast every 7-10k miles, then even a little dust getting through to the engine (if that is what many people above may have proved that K&N filter may let through) should make no horrific / significant difference.

I have a 3 Series BMW and definitely plan to change to a K&N filter.

September 4, 2009 at 10:42 am
(174) Melanie says:

So… what were the results of the Accord Wagon test? I could care less about all the details and masculating car lingo left in previous posts. I came here to find a simple answer whether the K&N filter improved Horsepower and possibly fuel economy. I see no experiment results from Aaron.

September 24, 2009 at 4:09 pm
(175) Johnny says:

Yea, exactly. What were the MPG Results?

September 29, 2009 at 4:20 am
(176) ag says:

3 years 4 months 11 days…… wow… i think this is a new record… call guinnes book of record.. the longest thread ever….

October 7, 2009 at 5:18 pm
(177) MidpacMopar says:

I’ve used K&N filters on several vehicles and I have no complaints. Significant performance gains were especially noticed for a 4cyl turbocharged performance car that I used for street & track use, as it increased intake airflow which allowed for quicker turbo spool up.

Throttle response was significantly improved for all vehicles that I’ve used them on (1 car with a turbo, another car that ran with nitrous, and 1 naturally aspirated truck).

I obviously didn’t purchase K&N’s to save fuel. You want to save fuel? Go buy a hybrid -OR- Watch your speed & properly maintain your vehicle (Tire pressure, synthetic oil, etc.) on a regular basis.

As for maintaining a reusable filter – I enjoy tinkering with what I drive, it’s half the fun of it. K&N reusable performance filters have worked well for me for competition as well as for daily driver use.

SO…In defense of K&N’s products (And no, I’m not sponsored!), they get a thumbs up from me.

October 11, 2009 at 3:10 am
(178) BC says:

After reading this entire blog, no one must have gone to this testing web site on filters. Unless I misread the data AC Delco makes the best filter. Look for your self.

October 11, 2009 at 3:12 am
(179) BC says:
December 15, 2009 at 9:24 pm
(180) Solara says:

OK… I read 3/4 of this post last Sunday night. Wow.

I went ahead and installed a K & N drop in filter on my car this morning and have driven it about 50 miles freeway/city today. My “test” vehicle is a 2000 Toyota Solara 2.2L 5 Speed Manual with 150,000 miles. 75,000 miles were put on by me, most of them in a single year – job related. I’m very familiar with the “real world” performance characteristics of this vehicle.

The car hasn’t given me a reason to replace it, so I recently had it fitted with new, slightly stiffer struts, premium H rated performance tires and a trip to the body shop to restore the coachwork. The car handles well, averages @ 28 mpg and is fun to drive. If the K & N Filter provides a noticeable, inexpensive performance upgrade – good enough.

My take-away: The car has a noticeable increase in torque and throttle response following the K & N filter installation. I suspect this cars modest initial horsepower rating makes a slight performance gain more detectable than in higher horsepower vehicles.

I’ve analyzed the air filter test results that verify higher particulate pass through for the K & N. This car receives a synthetic oil/filter change every 3000-5000 miles. I don’t anticipate the K & N, in conjunction with this oil change interval, will promote an appreciable decrease in engine service life.

I most likely will not be fitting a K & N drop-in to my low mileage Dodge Durango Hemi, unless I verify a significant increase in mpg on the Solara (not anticipated based on information presented at this post).

Mission Accomplished.
(My real sports car went to college(s) – so far!)

December 29, 2009 at 7:30 am
(181) sms says:

I can see that this has been going on for long time but i need to explain my experiences.

My uncle who has had over 50 years experience which includes 11 state titles and 1 national title and myself over 20 years experience in motocross riding. I can honestly say the only filter that is used in motocross are oiled air filters. Which i must say are used in one of the most tuffest and trying conditions. These filters which include K&N, UNI and other brands sure they may allow a little more dirt through but i can tell you these machines don’t stuff up because they get too much dirt in the motor they only stuff because they run at such high revs they just wear out.

I Don’t have any association with any filter company, neither do i get sponsored by them but alot of the comments made by people on this forum about K&N and other brands is incorrect. These filters are fantastic and for conditions that they are used in they would not be beaten by the normal paper filters. Sure the paper filter doesn’t allow as much dirt but there performance is lagging and do not live up to the K&N and other brands.

You think, if these filters were no good they certainly wouldn’t be running them in the motocross bikes and other vehicles. No matter what anyone says about car companies they sure won’t spend the extra money to put these filters in thier new vehicle because i can assure you they are trying to get out of it as cheap as possible.

February 17, 2010 at 1:33 am
(182) Resham Karnavat says:

I have used a Filtek centrifuge oil filter in my trucks & FilterMag in my cars, real satifactory & economic results.

February 20, 2010 at 7:01 am
(183) Rick Pich says:

Wow, this thread is almost four years old and still going strong. Since I’ve found this thread to be so helpful, I felt compelled to help keep it alive by at least by commenting what I got out of it. Good job Aaron (although I gotta say you’ve been awfully quiet the past few years).

Anyway, I’m not an engineer, I’m not a racer, I’m not a mechanic, I don’t rebuild engines, and I don’t know what a dyno is (and I probably misspelled it). I’m just an average Joe (in this case Rick) who can barely change his car oil. I came across this thread because my car is due to an air filter change, the dealer wants to rob me blind and aftermarket filters (except for K&N) aren’t available for the model yet.

I’m hesitant because the claims K&N makes reminded me too much of snake oil salesman. So I figured I’d do some research/reading before taking a chance with K&N or obliged to being raped by the dealer. I don’t care about power gain, and I’m skeptical of any efficiency claims without unbiased, trusted, scientifically verifiable third party data. All I want is an air filter, one that filters air. Not one that makes my car growl like a drunken tiger, or promises to make my wallet grow to the point I’d suffer back problems from sitting on a lop sided butt because my wallet has grown so fat. Just a plan and simple air filter that works and do not cause side effects in the process.

Unfortunately, after reading through 4 years of comments from emotional K&N supports, skeptics and “experts”, I think I’ll head to the dealer and consent to being raped and robbed. Don’t get me wrong, it’s not about being cheap or not being able to afford it, otherwise I wouldn’t have bought a brand new car which you can’t even get aftermarkets for yet. It’s more about principles. If I can change my previous cars and wife’s car filter for $10 to $20 builds, and the cost difference can’t be justified with labor since the task is so simple, how does a does a dealer justify charging many times more for the same thing? Principle aside, I’m not taking a chance with some of the problems I’ve read about here. So, with my head hung low, I now head out the door to dealer….. thank you sir, may I have another :(

February 24, 2010 at 3:05 pm
(184) Michael Herman says:

I’ve decided to do my own K&N vs. Fram testing. Unfortunately, the weather hasn’t been too cooperative, being in Oregon during the winter.

At the local Shucks, they had a setup with fans, a tube, and a ball. You could switch the K&N panel filter for a Fram of the same size, and see the difference. No contest, the K&N flowed MUCH better, pushing the ball against the top. The Fram filter barely moved it.

I drive a 1991 Ford Tempo. Low power and fuel economy in comparison to today’s 4-bangers. I’ve had the K&N in there since I got it, along with some other intake mods (enlarging the trumpet in the plenum to match the throttle body size), and it has some getup and go at the low end. After I put the Fram back in, it quit 3 times before I could even get out of the driveway. The ECU didn’t recalibrate for the difference in flow yet. This was telling me that my injectors were putting more fuel into the cylinders, expecting the higher airflow from the K&N filter.

This leads me to conclude that the K&N air filter causes fuel-injected cars to use MORE gas than with a comparitively restrictive paper filter, therefore lowering fuel economy.

Now, to read the other blogs to see what my results compare to.

February 27, 2010 at 2:26 pm
(185) Davo says:

Wow! I am stunned by the wide and varied opinions about air filters. Throughout this entire thread, there has been a huge amount of discussion concerning improved performance/gas mileage. Unfortunately, there has been VERY little mention about the effectiveness of how well an air filter actually filters.

The operative word in “air filter” is FILTER. Some of the most expensive and high performance engines that are made (especially those used in military engines that operate in desert environments) use synthetic air filters to minimize the smallest sized particles from entering their engines.

While an increase in mpg or performance would be nice, my ONLY goal in choosing an air filter is to keep as much air borne particles out of my engine.

I recently put out a few extra bucks for a K&N air filter and noticed an immediate improvement in acceleration (which is NOT the reason why I bought the K&N filter). I was under the impression that these filters were excellent in filtering out the smallest of airborne particles (after reading over this thread, it appears that impression was wrong).

There have been postings on this thread lodged by a K&N marketing executive touting the qualities of their filters. However, there has NEVER been ANY mention about the effectiveness of K&N filters ability to minimize fine particulate matter from entering the engine. Why is that?

My question: What is the percentage of K&N’s air filters ability to filter fine particulate matter (and what size do they ACTUALLY filter out) and what test was used to determine the results.

Funny how this thread is so many years old and no one has asked this question.

Unless I have some test results performed on K&N air filters done by independent labs, I’ll be removing mine and sending it back to the corporate headquarters and will demand a refund.

PS: Thanks to whomever started this thread.

March 12, 2010 at 2:02 pm
(186) scott simmons says:

“to filter or allow air flow, that is the question…..” or perhaps not, maybe it is just a balance of the two. I wish to add my experience, I hope others find it helpful.

I have a 2000 Chrysler 300 that recently turned over 325,000 miles. I live in Delaware and work in Philadelphia, the middle of the east coast and not the cleanest air in the word. This car has been everywhere from Maine to Florida (many times). We used paper filters for the first 44,000, at which point I installed a K&N. I am good about monitoring gas mileage, and can say with some certainty there is no difference in fuel economy between the two styles of filters. The mileage I get now is the same as it was 8 years and 280,000 miles ago, no better but no worse. I will also state that there may have been a very slight improvement in performance, but probably just in my head and really nothing measurable. The flip side is that concerning how well it filters, I have to certainly answer well enough. After many, many miles my engine has not succumbed to any nasty effects from letting in dirtier-than-paper-filter air either. I regularly use the Chrysler dealership for maintenance, and none of the tech’s that work on the vehicle have had anything bad to say about the filter and they know the car well. There are (30?) year’s worth of these in the field, it seems a pattern would have emerged if they were truly villainous. Their use will not void a factory warrantee. Unless you are anal about EVERYTHING about your car, gas, maintenance, etc. experience tells me the filter will not impact engine life. I’d worry more about “dirty” or bad fuel, yet how many of us can be particular about where we tank up 100% of the time?

My conclusion is that I the K&N filter does not significantly improve performance, and that it filters very well or at least to standards that should exceed what is necessary to maintain your vehicle well. I would not expect it to cause engine damage or loss of mileage due to poor filtering. In my opinion your personal decision should come down to cost*, waste, and convenience of proper maintenance. If you plan on driving your vehicle less then 50,000 miles why consider an expensive filter when there is little tangible gain? On the other hand, if you plan on buying 3 or 4 or more filters, then why not save some time and money and get a long term solution?

Personally, even with the cost of the cleaner kits I have saved a lot of money on filters alone. Add to that the positive endorphins’ that come with “going green” and using a recyclable product. Yes it is easier to just pop in a paper filter, but the K&N is not that hard to clean. I only need check it a couple times a year, and don’t have to drive to the store to by a new one.

*cost – I just purchased a 2005 Escape. The Ford dealership price is $24.95 for a paper filter, the K&N is under $50.00 delivered from at least two internet sites. In this case the decision is easy.

Thanks also. This is a truly interesting posting with varied opinions, I guess we can add “air filters” to the list subjects to avoid at social gatherings along with religion, politics and in-laws…

March 18, 2010 at 5:46 am
(187) Arnica says:

“I guess we can add “air filters” to the list subjects to avoid at social gatherings along with religion, politics and in-laws…” (scott simmons)

i totally agree with you…


March 19, 2010 at 4:19 pm
(188) RCH22 says:

I just stumbled on this thread. Way early on someone asked if any manufacturers use K&N “Type” filters. Well, for those who don’t know, Toyota has a reusable air filter available through their Toyota Racing Development branch.

It costs about $30-40 more than a K&N, and their cleaning kit is about double the price. I asked the parts guy what the difference was between the K&N and TRD. The answer was the oil in the TRD is thicker, so it doesn’t run down to the MAF like a K&N will. I chuckled.

Now I doubt that’s really true – but if it is, I guess if you used a TRD they couldn’t say the MAF failure was caused by an oiled air filter. Either way, I think the oiled filters are fine and do present a long term cost savings. Just don’t over oil them.

April 5, 2010 at 7:41 pm
(189) D Man says:

So I have spent the past hour or so reading this whole thread. Its a great debate but in the end our buddy Dave tells us that the main benefit is that you dont have to repair the filter as often PERIOD. He doesnt claim any mpg increase and even fueleconomy.gov says that air filters only offer performance increases, not better mpg unless you are using a carburetor as seen in the classic cars of yesteryear. Also he doesnt claim that the filters increase HP either. He says the whole point of the filter is to save you the cost of replacing it that often. But really it comes down to are you going to buy the name brand item or the walmart brand? Some people might think the walmart brand is as good or better like many after market parts, while the brand name could be considering playing it safe, but Dave is pointing out that clearly the main benefit is the long life. Personally I do all my maintenance that is possible and I would rather spend less for a standard pop-in then more in one shot for something that to me has no real benefit. And finally for the people who claim that the high end car companies dont use the filters for a reason, these vehicles have sealed transmissions and are made so they have to be brought in so there can be profit. Why would BMW buy someone elses product when they can use their own and make more money?

April 17, 2010 at 5:44 am
(190) WhizzMan says:

Clean filters do provide a better gas mileage. Here’s why: When an ECU for a specific car is being tuned at the factory, they use clean, OEM filters. These provide a certain flow restriction that is not linear, but depends on the amount of throttle given and the RPM of the engine. The entire ECU is set up using these figures. Yes, the ECU has a correction factor for air/fuel mixture, but that is a linear factor that is being updated by measuring the exhaust fuels with an O2 sensor. If you clog the filter, you will restrict air flow non-linear. There is no way you can correct that with a linear value using the O2 sensor.
Most modern cars do have a true throttle position sensor, the ones that only used switches have not been sold for over 15 years. So yes, the amount of foot you give it usually is interpreted by the ECU as an indication on how rich to make the mixture. Going full throttle requires a richer mixture than coasting. Even if you correct linear for a clogged filter, having to depress the throttle further will have the ECU mix richer, making your fuel economy suffer.

May 10, 2010 at 8:59 am
(191) Michael H says:

I use a K&N air filter. Just to let you know…I could tell a difference in HP as soon as I started my car with it in. I have a 2002 Mustang GT. I put the K&N in my car when it only had 5000 miles on it. My car now has 155,000 miles on it and it runs like a brand new engine. I have charged the filter 3 times during this period. If you want a real world test I have your test. The only thing I have done to the engine is I had it tuned up around 100,000 miles (plugs, wires, fuel injector service, throttle body cleaning). So if you are worried that a K&N will not do the job of a paper filter you are sadly mistaken. If there were an issue with filtration of a K&N as some of you say on here my car would have stopped running long ago. I have to tell you that my car does not burn oil or knock, nothing like that at all. Your engine true source of longevity is in changing your oil in a timely manner. So you can take your paper filters and I will still outlast you on the road. My $49 compared to your $$$ of replaced paper filters up to 150,000 miles. K&N real world tested from NC to FLA to SC back to FLA and now back in NC and everywhere in between.

May 22, 2010 at 3:49 am
(192) Karl says:

You guys need to get off of your butts and go down to the K&N factory for a tour.
Of course revenue stream is an important factor in making perishables for an automobile It’s a huge industry which K&N is a small part of.

David outlined the differences between paper filters and K&N very simply. Why would he go to so much trouble to try and bullshit everyone? Perhaps their are companies out there that make products that do exactly what they say!
I’m sure David could organize a tour of the factory first hand for a small group.

To me a K&N filter just makes more sense and the brand has been around for ever. As a layman the physics principle makes perfect sense to me and when you hold one in your hands you can tell it is a quality build and very nicely made. Who would go to so much trouble to make such a nice product and then have it stuff up your engine? It’s starting to sound like a bizarre conspiracy. These guys are auto enthusiasts as well. Yes they are a business but they certainly want to stay in business. Really you could go on splitting hairs for ever. If your happy and comfortable with paper go for it keep using them, they do the job.

Most of you trying to bag K&N in this forum have no way of proving your speculative claims. The only person who has data to support what they are saying is David.

Happy motoring!


(Elfin Sports car Enthusiast from Australia and Son of a motor racing journalist)

May 22, 2010 at 3:50 am
(193) Sally says:

Interesting thread!

May 22, 2010 at 3:57 pm
(194) Karl says:

Of course revenue stream is an important factor in manufacturing perishables for an automobile. It’s a huge industry of which K&N is a small part. The more perishables the better the revenue stream.

David outlined the differences between paper filters and K&N very simply. Why would he go to so much trouble to try and bullshit everyone? Perhaps their are companies out there that make products that do exactly what they say!

In my opinion a K&N filter just makes more sense. The brand has also been around for ever. As a layman the physics principle of a K&N makes perfect sense to me. When you hold one in your hands you can tell it is a quality build and very nicely made. Who would go to so much trouble to make such a nice product and then have it stuff up your engine? It’s starting to sound like a bizarre conspiracy has been hatched. These guys are auto enthusiasts as well. Yes they are a business and I’m sure they want to stay in business. Really you could go on splitting hairs for ever. If your happy and comfortable with paper go for it keep using them, they do the job.

Most of you trying to bag K&N in this forum have no way of proving your speculative claims. The only person who has data to support what they are saying is David.

Happy motoring!


(Elfin Sports car Enthusiast from Australia and Son of a motor racing journalist)

May 22, 2010 at 5:52 pm
(195) Woody says:

I bought a second hand K&N on eBay for my Honda Accord. It had been cleaned and oiled using the K&N recharge pack. A perfect filter for half the price. I noticed a performance lift straight away. I assume K&N can’t make performance claims due to legal reasons. I love the fact that they can be used over and over again.

May 30, 2010 at 5:19 pm
(196) another Mark says:

I read the whole thread, wow! Some folks have given great analysis, others IMO, not so much. I don’t pretend to be the final arbiter, but I have studied the issues for 30 years. Perhaps I can help some to understand better? What I think is missing here although many made the point that the engine management system just doesn’t care or even know the difference between the restriction of a partially closed throttle plate and a restricted intake system. And some folks alluded to the fact that the system is a closed loop and many of us know what that means, but others perhaps do not.

So here is as simple as possible an explanation for those who do not. As soon as a modern fuel injected engine warms up the O2 sensors, (which is very fast), All of the sensors that feed information to the Engine Management Computer (MAF, IAT, TPS, MAP RPMS), provide only an estimate of how much air is flowing through the engine and therefore how much injector on time, (pulse width) is needed, in other words how much fuel is required to create a proper air fuel mixture. This estimate is then altered based on information from only one source, THE O2 SENSORS. The O2 sensors tell the engine computer in real time whether it’s estimate, based on preprogrammed look up tables, (fuel map) is producing the expected fuel air mixture. If the O2 sensors say no we are too lean, i.e. too much air then a multiplier is added to the estimate to add a little fuel. If the O2 sensors tell the computer that we are richer than expected then we subtract from the estimate of injector on time to take away fuel, recheck the result at the O2 sensor and recalculate every few milliseconds. Over time the computer stores these corrections to the estimates so that it’s estimates will be better over time, Computer Learning).

Unless we are in open loop operation which in modern engines is generally less than 1 minute after startup, relatively small changes in intake restriction in either direction will have zero effect on mpg or hp. The only exception to this would be at wide open throttle were less restriction would equal more air, but at wot we are also not in closed loop any more and the fuel tables are quite a bit richer than non-wot operation.

Want more power? Step on the throttle harder. Want better fuel economy? Keep your foot off the throttle, (accelerate more slowly, decelerate more gently and let a little speed bleed off when climbing a hill). If you are going to field test any modifications that you choose to make, give the computer 1,000 miles and at least three driving cycles to adapt to the changes in order to make your findings apply to long term effects. The reason for this is the aforementioned Computer Learning. I think this point deserves repeating. You may notice a change in performance from a modification for the first few days or the first few hundred miles but then those changes in performance go away as the computer adapts to the changes and anticipates the necessary fuel adjustments. In other words you may be able to make the engine run a few percentage points leaner or even richer for a short time and therefore create a noticeable change in performance or fuel consumption.

Unless the modification is outside of the computer’s ability to compensate, the performance change should be temporary. Of course changing the computer itself through programming chipping etc is a completely different conversation, as is turbos and super chargers or major modification involving compression ratios, intake manifolds and headers cam shafts etc, but then again these changes really make your engine a different engine than it was before and will generally require changes to the computer program. These types of modifications alter the volumetric efficiency of the engine, generally improving it at higher rpms and decreasing it at lower rpms, It’s possible to go the other way as well.

An engine which has been severely altered may in fact have inadequate intake air available from the stock system in which case a modification of the intake air system may be necessary.

Bottom line. Unless you have a modified engine or engine management system or an older vehicle that does not use O2 sensors in a closed loop fuel management regime. You are not at all likely to get long term, measurable increases in mpg from intake modification or less restrictive air filters. It is entirely likely that you will get better acceleration with less throttle depression, (which many perceive as an increase in performance). You are almost certain to get a small increase in peak horsepower, which is a driving condition that the average driver will never experience for more than a few seconds on rare occasions such as passing several cars on a two lane highway or merging into heavy traffic on the interstate.

October 14, 2010 at 9:32 pm
(197) Scott says:


Thankyou for your explanation. Yours has been the best so far. Btw, I do use a k and n, but only because it is re-usable.


June 4, 2010 at 11:37 am
(198) Marcelino says:

I don’t know who has scientific evidence, but research based on empirical evidence comparing both filters should be conducted using a good sample before arriving at any conclusions. My experience with the oil filter is that it works, but I wouldn’t talk about efficiency or fuel economy, since there isn’t any data concerning this issue. However, I change my oil normally and the is no difference from before using the new oil filter. no dust or dirt inside. …Nevertheless, I am now using a pre- filter just in case.

June 8, 2010 at 7:30 pm
(199) Valori says:

I’ve had a K&N air filter in my 1987 Toyota pickup
(carburetor 2.4L) for about 5-6 years.
Initially I did not notice any gains in power or gas mileage. It is still the same, no improvement in either area. I guess it’s a question of upkeep and if you want to change filters.
I for one, will probably stick with regular paper filters and change them out at regular intervals.
Instead of spending $50 on the K&N, buy filters when on sale to stock up.

June 18, 2010 at 9:53 am
(200) ryan says:

My K&N filter should be arriving today. Since I have onboard computer that calculates my MPG, I will post the results of any changes in MPG after installing the K&N filter. Hope this little test will conclude any questions about filter giving better MPG. I don’t have a lead foot and my driving habits are pretty much consistent (slow accel and etc).

July 2, 2010 at 9:51 pm
(201) Ryan says:

I just got back from my 430 mile beach trip. On the way to the beach, I’ve used K&N air filter with Vortec Cyclone gas saver and achieved 21.2 miles per gallon on the highway doing 62 – 65 MPH. I was please since I drive 2007 Lincoln Navigator 4X4. Original sticker EPA MPG rating is 18MPG on the highway. So I figured I did 3.2 miles better than the EPA rating. YEAH!

On the way back, I did a pretty interesting test. first 60 miles, I ran with K&N air filter only to see what type of gas mileage I would get. Result was 20.3 MPG doing 62 – 65 MPH. I was little disappointed but thinking hey.. this is 2.3 MPG better than the EPA rating. Here is the killer.. for the next 60 miles, I ran straight STOCK Filter only and…. I got 21.4 MPG!!! doing the same speed.

I have pictures of my speedometer, computer and odometer readings. I’ll post them on my blog and give you all links to them.

So, my conclusion is that K&N air filter DID not give me better MPG. I really didn’t notice that much of power gain either. Stock air filter did MUCH better. Also, Vortec Cyclone DOES NOT WORK!! Good thing I have 120 days money back guarantee on it.

July 9, 2010 at 12:24 am
(202) Michael H says:


Does your onboard MPG calculator give you instant feedback? That test leaves a lot of room for a wide range of variables.

July 12, 2010 at 11:22 pm
(203) Ryan says:

Michael, yes it does have instant feedback. Here is the link to the pictures of my dash with MPG.


It was pretty sunny day with no head wind on the way back. Also, interstate 64 and I95 in Virginia is pretty flat both ways.

August 1, 2010 at 4:08 am
(204) mark says:

whissman, ryan,

Throttle position sensors do NOT have much to do with mixture. Once you understand this, and clog your filter as much as you want, you will find no change in gas mileage go ahead , do the test . on your next 200mile trip, stick a diaper in your intake. It might take half throttle go go 60mph, but your gas mileage will not change at all.
Ryan, your test is hardly scientific.

I wrote this a while ago, and it still is true today:
You guys still dont get it. “Throttle” means “choke”!! This means that the throttle is the restriction. the ecu has not a clue of most throttle postions besides wide open throtttle and idle. If you understand this, keep in mind that the Fuel managment system provides perfect mixture based on air flow meetering, and O2sensor information. IF i clog the air filter with a diaper, the car will have no power, and may need 1/2 throttle just to go 55mph, but your gas mileage will be the same. Rich, this is because the clogged air filter is now creating the restriction that the throttle plate doesnt have to. the end result is a power level, (cruise at 55mph for example),and fuel flow rate that would be equal with or with out the clogged air fliter.
In the end, air filters have NO bearing on fuel economy. The EPA is giving us BUM advice and it is a crime! In fact, the world could save millions of gallons of gas, if everyone would just let their filters get diry! As long as the dirt doesnt enter the engine, there is no issues, but a loss of power!
If you make more power, you make more Gas. Pretty simple stuff!

August 6, 2010 at 9:51 am
(205) Scott59 says:

I don’t have measureable performance or mpg gains, but I have used K&N filters in all my cars for 20 years with no problems. Examples: 1985 Saab – 170K miles no engine problems, 1991 Mazda Protege 160K no engine problems, 1996 Dodge Caravan 130K no problems, 2000 Chrysler Concord 175K no problems – my son is still driving this car, 2006 Sienna 75K runs like new – wife still driving. When I buy a new car, at or before the first air filter replacement I put in K&N. Used cars I put in K&N when the old filter is dirty. One comment about the recharge economics, the recharge kit is good for a few recharges, and cleaning/recharge typically only needed every 50K miles. I think the K&Ns pay for themselves if you keep a car more than 100K miles. I don’t know if it’s the K&Ns, but I always beat the rated MPG numbers, even at 75-80 on the highway.

September 8, 2010 at 12:53 pm
(206) Sporty7g says:

Reading your “Can a better air filter improve fuel economy….” left me disappointed. All I read on the web, in forums and in blogs like yours focus on either performance (meaning horsepower (hp), acceleration, speed, and torque), OR…..OR meaning gas mileage. Let’s get real! These are NOT the most important metrics for a filter folks! The principal, the dominant purpose for an air filter is to keep dirt out of one’s engine, thus prolonging it’s life by minimizing wear. It’s is not a question of can I get better mileage or get better “performance”, because with electronic fuel injected vehicles, getting more torque and hp works at cross purposes to better economy. If a “performance” filter does it’s intended job, it allows the engine to breathe more air when asked (like the K&Ns). Right? Well the ECU will sense greater air mass and will increase gas flow to maintain the proper air-fuel ratio. More air through a filter means more gas consumed, temperature not being considered for the moment. To get better mpg, the engine has to use less fuel, and thus less air, because of the need to maintain the proper mixture ratio. There is a test, called ISO 5011, which is used to evaluate air filters for (at least) the two important parameters: filtering dirt and passage of air. A truly great filter will be the best compromise design and best materials allowing the least amount of dirt into an engine, while passing as much air as possible. Please remember to tell readers about protecting engine cleanliness. Thanks.

September 12, 2010 at 7:20 am
(207) joe c says:

i’ve just spent the better part of the morning, and downed a pot of coffee reading most of these posts – there’s a couple hours of my life i’ll never get back. not to get into a pi$$in’ contest about K&N, factory OEM filters, airflow, increased MPG, or what ever, let me point out several facts -

the effect of filtering – most people dont keep or drive their cars long enough to worry about wearing an engine out. after 3, 4, or 5 years, and 60 or 70 thousand miles, we’re tire of the bucket of bolts and move on to a new ride, so who cares about every microscopic bit of crap the t might get sucked into an engine.

cost savings by not having to buy those relatively inexpesnive paper filters. you’ve got to be kidding me. ever clean a K&N? what a royal PITA that is. give me a disposable drop-in anytime! with the cost savings, don’t forget to add in the $10-$20 cleaning kit – go back to the keeping your car for 3-5 years and the 70K mile thing – what cost savings? i always figure “my time is worth $20 hour”, there’s no way in hell, and after 4 years, i’m ditching my ride for a new one anyway. so, how many times is the average owner going to change their air filter in a car he keeps 70K miles – maybe a couple times at best.

performance – another “you’ve got to be kidding me” thing. if you pick up any HP, its at higher RPM, and most of us live in the “below 3000 RPM world”, so that 3-4 HP gain is insignficant. so, who really needs it.

those after market performance air filter do flow more air, but it’s not the flow rate of the filter, but the air requirements of the engine. a OEM paper filter meest and exceeds the requirements of the enigne. change the filter at the manufacturers recommended intervals, any everything’s fine.

marketing director’s job is to sell products – their bonus check depends in it!

performance air cleaners, like fancy motor oils, sparkplugs that defy the laws of physics, wax, polish, and microfiber towels – 90% hype and 10% fact…

finally, nothings free – simple law of physics!

October 28, 2010 at 6:00 pm
(208) Andrew Scott says:

Bottom line, its just an air filter thats good for environment, of which you americans know very little about, pull your heads outa your asses. Most american cars waste a lot of fuel, produce very little horse power to the amount of fuel (gas) they use. an air filter is going to do very little in the way of improving the horsepower of poorly made american gas guzzlers.
if your going to worry about miner details then maybe you should start attacking Dodge as there cars can’t conner for s**t. K&N filters work better in european cars as the fuel in Europe is better having a higher octane level, thus with better air flow from the filter the fuel is used more efficiently – which is why K&N are used in performance motor sports.

Andrew Scott
Lotus cars

October 30, 2010 at 4:53 pm
(209) PittsburghJames says:

I popped in the cheapest air filter I could find into my Tiburon’04. It was eating up lots of fuel compared to my Hyundai Genuine air filter. So being tired of this – I looked into an alternative. Since the K&N wasn’t too much more than the Genuine air filter, I decided to go for it. Had it for about half a year now. My engine purrs slightly differently. (2liter, 4 cylinder)

From the crappy air filter, I noticed major fuel efficiency improvement. (Yeah, I understood the inverse relationship of air quality (free of dirt) and air flow). Compared to the Hyundai genuine part there is a small improvement.

I stand by the K&N filter. Also, I plan on selling or trading in my car before it sees +50,000 miles (~3 years). However, if I had to chose again – I might just buy the Hyundai genuine part.

BTW: Wow, this thread has been actively going on 4 + years.

November 4, 2010 at 1:48 pm
(210) Dennis says:

Wow! Ask a question and get loads of analysis and emotion. I just bought a 2010 Dodge Ram 1500 with the 5.7 Hemi engine (dual exhaust). I was looking at a K$N conical air filter system and found this string. Read most of it, too tedious to get through all of them. Good info, though. Obviously, on balance, these filters are good enough for racers to use them in most cases, and aviators typically don’t care how much things cost, but for some passenger cars/trucks these may not produce results that are that much better than OEM filters, especially if you’re the type who does your maintenance on time. I was (and still am) leaning toward buying and installing one, but when I re-looked the owners manual (actually a CD) for my vehicle, I got a surprise. Starting at 12K miles, and in 6k increments after that, my manual says if you have been driving in dusty or off-road conditions CHECK the filter and replace as necessary. It does not specifically say to replace it until 30K.

Hell, a lot (most) of the stuff they sell at speed shops is stuff you don’t really need right? Bottom line the K&N looks cool, can be said to be an environmental benefit, may get you a lttle more power, may make the engine sound a little throatier, may even make you think you’re getting slightly better gas mileage. If that’s enough justification for you, pull out the checkbook or plastic and have a ball. If not, there’s not much wrong with OEM and putting the money into something that pays real dividends, like beer.

November 7, 2010 at 4:18 am
(211) John says:

Wow that was allot of reading. I am building a small airplane and was about to throw down about $300 for K&N filters and adapters to fit my carburetters. I will be landing on dirt and grass strips and don’t want any extra dirt in my engine I think I will be using a paper filters. Thank you for your comments.

November 26, 2010 at 3:07 am
(212) anna says:

I love my car :)

December 25, 2010 at 9:53 pm
(213) mark says:

Pitts James and expecially arrogant Andrew from over the ocean,

You guys STILL dont get it do you . the air filter has NOTHING to do with fuel economy. I ONLY effects how well it cleans the air to the car, and hom much HP you lose in doing so. again, and Ive been saying this HERE for 4 years now. “Throttle” means “Choke”. the throttle is choking the engine to reduce power and allow you to cruise to better mileage. if you choke with the throttle or a clogged or restrictive air filter, the air doesnt know the difference. :)

Now, andrew, as far as american cars not handling well, that all depends what american cars you talk about. go take on a viper or a Vet at the track and see how you do in a similar year car.

February 5, 2011 at 7:26 am
(214) Riggo says:


Hi Guys,

Anyone who can help me?…more so, recommend.

I’m planning to buy an air intake for my 1993 Isuzu 3.1D Trooper A/T. I’m more likely to purchase a K&N (well, having gone through some threads and blogs). However, I have the following concerns…
1. Should I purchase a cold air intake and not RAM?
2. Is CIA or a RAM different at all compared with the so called snorkel?

Please help. My aim to is add some HP and, if lucky, add more efficiency in my fuel consumption.

Pardon for all these questions. I’m a newbie! :)


February 27, 2011 at 2:12 am
(215) mark says:

Do the CIA or RAM for one reason and one only, to increase HP. It WILL NOT increase any efficiency for fuel consumption.

April 22, 2011 at 1:59 am
(216) fc says:

I cant believe i read this whole thread, argument, debate or whatever it is…… First of K&N drop in filter’s purpose isnt to increase “MPG”, its purpose is to save you money on the long run . You buy one K&N filter and never have to buy another filter again. And its just a reuseable filter its not gonna give you any hp, anyone who claims they did is more of a mind over matter thing. Cold air intake kit works a little different, I believe its purpose is to give your engine a faster reponse since it will suck in air faster than oem and mix with gas quicker , but no “hp” gains . The cars computer reads the air/ fuel mixture, but has its limits….. If your looking to gain power through your intake look into force inductions as in turbo charger or super charger, these work with air and fuel mixture but ofcourse you have to get bigger injectors that shoot more gas to mix with all the air you will be blowing in your engine. One of the easiest way to wake up your engine or save gas is getting a custom tune or programmer.

May 6, 2011 at 8:08 am
(217) Tom Baker says:

My son has a GMC Envoy and it had an injector fail. We removed the intake manifold (no small task) and we were shocked at the mess inside the manifold. The inside of the manifold was coated with a sticky, honey like mess that was up to 1/8 inch thick in places. It was a thick oil, mixed with dirt that was present throughout the entire air inlet path, however it had mostly collected at the lowest point where the plastic intake manifold bolted to the aluminum head. Greg bought this truck used and it has a paper element in it, so it must have been a previous owner who used an oiled type filter. The clean up is a mess, it may have contributed to the failed injector, (all six were coated badly in that crud) and it would have cost thousands in a shop had he taken the truck in . Mind you, this is not an old truck. 90 K and it’s 6 years old. I work on a lot of cars, I’ve been doing it for 25 years and I even put a K & N in my wifes Monte Carlo. I know what the charge oil feels, smells and tastes like and that’s the junk in Greg’s intake manifold.
My point in telling you all this, is that while you can argue the value difference of the oiled gauze vs paper elements in pennies per year, the potential damage from the oiled filters is real if the element gets over serviced. Yes, you could say that any repair or service done incorrectly has the potential for causing damage, but no paper element could cause this. If you like them, use them but follow the instructions carefully. If you buy used vehicles and it has one, look for evidence that the element was over serviced. Also, do some internet checks on damaged Mass airflow sensors from over serviced oil charged gauze air filter elements.
Final thought…I will be putting paper elements back in the Monte Carlo. In my opinion, there just isn’t any noticeable difference in performance and it makes me sick thinking that I may have caused a similar mess in my wife’s car.

May 18, 2011 at 12:36 pm
(218) I cant believe I just read all that says:

After reading this whole thing, my mind is still not made up. There are many arguments on both sides.

Note to the author: Good idea asking the marketing director of K&N to post on here as well, its not like he has a biased opinion of anything, since he works for the company. (FYI: Its hard to convey with words, but this is full on sarcasm.)

The conclusion I came to is this, buy a K&N filter, then get every last bit of oil off of it. Oil it myself with as little oil as possible, and let it dry for an extremely long time, then, get a piece of fine mesh material (example: screen door material) and connect it behind the filter for a while. if the oil really comes off in huge amounts like people claim it does, it will get caught, and I will remove the filter.

June 23, 2011 at 1:42 am
(219) ? says:

I like My K&N intake, I have not had any problems with it or my engine going bad. Quit trying to scare people out of buying K&N products.

And to the Original poster,

You started this thread in 2006 it is now 2011, lets get those results up ASAP. What happened? Did the K&N work so well that you are still on the same tank of gas?

September 12, 2011 at 4:57 pm
(220) Dru says:


August 13, 2011 at 8:15 pm
(221) JB says:

If you’ve made it this far down the thread, bottom line is unless someone tests every after market air filter in a controlled environment and the air flow testing is done at the micro level by computers to determine the amount of dirt that is passing through each filter after considerable use, there is no concrete answer.

Sounds like the next show for Mythbusters.

September 12, 2011 at 10:00 pm
(222) Steve says:

I’ve had a K&N filter in my 98 Civic for about 8 years. It ran good in the beggining, but in recent years the car was running rough, and the air intake (fresh air into car) was stinking. So I removed the whole filter & pipe, and the area where it enters the engine. (I’m not a mechanic so I ave no idea of the names.) Anyway, It was filled with a greasy dirt sludge everywhere. It was obviously screwing up the motor. My cousin who IS a mechanic took a look and we tried to clean most of it out. I stuck my stock filtration tube and filter back on after that, and my car ran well again. So I’m a bit pissed that all this time I thought I was doing something good for myself and the car but it turns out I wasn’t. What a disaster. I will never use an oil based filter again. They DO damage your engine after many years of use.

September 30, 2011 at 5:49 am
(223) Josh says:

Holy God….the mother of all threads! I purchased a high-flow K&N kit that hasn’t arrived yet. I was talking to friend about it who told me it reduced engine life, so I did a little digging, which lead me to this post….Holy Crap! After reading the entire thing, I have come to the conclusion that:
The mpg/horsepower side of this debate is basically pointless unless you make multiple other expensive performance mods.
The filtration issue is the the key point for the average driver, both the potential for increased engine wear and the cleaning/recharging vs. the simple drop-in replacement are the factors to consider. Time spent on cleaning, plus a more mindful approach to oil-changes, etc…
All that having been said, the reason I will most likely return the kit without opening it when it arrives is the oil build-up/engine/ MAF sensor damage issue. Even light oils and light applications of them will experience travel from airflow. It doesn’t seem that oil transfer or the potential damage from it is avoidable. In racing engines that are frequently torn down, cleaned, etc…aircraft engines that are equally or greater rigorously maintained, oil-transfer would have to be a non-issue due to frequent inspection and cleaning. To the average driver, this level of effort simply wouldn’t be practical; or in many cases, affordable at all. I’m sure K&N makes a fine product. But it seems like selling Nikes to average Joes to make them feel like they’re pros….professional product, professional application.
All just marketing in the end.

October 14, 2011 at 1:23 am
(224) Joe says:

This discussion makes me so disappointed that I’m not incredibly rich. Mark and a few others have given everyone the correct theory explaining why a K&N filter won’t improve mpg, but folks won’t listen, and still buy these filters specifically to improve mpg.

I can see 3 things that really help K&N filter sales:

1. There are still so many folks around who learned to work on older cars that weren’t computer controlled (o2 sensor feedback loop), and never were able to understand the significance of modern engine control. Does a clogged filter affect mpg in a carburated engine? Yep! In a modern engine, no.

2. A K&N filter will improve throttle response. If you mash the pedal down 50%, you’ll get more air flow with the K&N. In modern engines, that will result in more gas flow, and you’ll go faster. My wife’s Mini Cooper has a ‘sport’ mode button. One of the things it does is increase the actual throttle position at each pedal position. The car feels quicker, as it should. You’re using more gas, and mpg suffers.

3. Human nature dictates that many who buy these filters to get better mileage won’t admit to themselves or others that they made a mistake.

So these things won’t improve mpg in properly operating modern engines at steady state. I still have questions about whether they will improve mileage in real world non-steady state. But if they DO improve non-steady state mpg, it could only do that by making the engine run leaner than designed. That can’t be good

December 4, 2011 at 12:48 pm
(225) FRED says:

I get the best Fram paper filter for my C-6 and I change it every 10K. I also change my Mobil 1 oil every 6K-Cheap insurance for clean air & clean oil and a happy motor!!!!!

December 5, 2011 at 12:02 am
(226) Scorpven says:

I stumbled upon this post as I was looking up performance air filters for my 2010 G37S.
Been using K&N filters since ’89 starting with my ’86 200SX, then in my ’92 Maxima, then my 97 Accord (which I still have with 290k km) and last in my ’08 Accord. After reading through some of these posts I went out to my garage and replace the K&N in the ’08 Accord with the original 2 week old OEM which I kept in the K&N box. Using a flash light I noticed small oil deposits on the MAF sensor assembly.
BTW none of my cars ever suffered any engine problems, I also oil change with synthetic oil every 6 months. I think I have nothing to loose staying with the OEM paper.

December 7, 2011 at 6:06 pm
(227) Larry says:

It is an emissions thing why they are not installed in factory vehicles!!!!Cali for Example(Not Legal in California or other states adopting California emissions standards)is on the label of a K&N Filter

December 13, 2011 at 1:19 am
(228) Alan says:

Hello, I been reading this and thought I should add my .02.
Been in the filter business for close to forty years and I notice
their are a few who are telling it like it is. Tim and Brewster are
correct. I had a filter tester some 25 years ago set up like a vacuum with cotton cloth over the hole with the vacuum pipe. K&N was very dirty. Premium paper was good. Amsoil oil sponge was better than both paper and K&N. Seems as though the dirt was goin right through the K&N. That’s the reason they did “breath better”. (Premium paper) is the cheapest and best way to go lest your a racer and like rebuilding your engines and can afford it. I use a Injen cold air intake with a conical filter paper medium made for Amsoil, by Donaldson which is not stock, cleaned every 25K X 4 times.
Donaldson paper is the same paper elements that protect all our military vehicles in the in the Mideast deserts. All I can say is buyer beware. See if K&N will warranty a engine. Good luck to those K&N fans!

December 13, 2011 at 1:31 am
(229) Alan says:

In my previous comment I forgot to add that Amsoil quit making the oil foam / sponge filters because of MAF issues maybe not with their own but they reacted to the bad press several years ago. I never had a problem with the oil foam on any of the numerous vehicles I had them in. I just went with the technology flow nano micronic filter paper which if good for a Apache or Abrams or any other military vehicle in the desert ( talc like sand ) is good enough for me.

December 23, 2011 at 2:50 am
(230) michael says:

I read the comments , and i must say they were intresting ! I have a 1980 jeep cj7 that ran great with no problems until I installed the KN filter and started having carb issues because of the dirt passing thru it . I much rather carry an extra paper filter for now on then run KN filters .
I thought maybe it was just the jeep witht he carb , so we installed one on the camaro with Tbi 5.7 , it took a little longer but eventualy we were cleaning it out , so thinking thats 2 older vehicles maybe on a EFI engine with a cold air intake it would work !
Well there was no diffrence in performance , no diffrence in gas , no diffrence in power and all I ended up with was 3 KN filters that were expensive and crap !
Just because I know some of you will comment that you seen dyno runs on hotrod tv , etc etc etc !!!! KN is a major sponsor that keeps them on air to show you what you need to spend your money on . If you want the power , torque , and or more mpg gas then do it the way real motor heads do it and build a engine !
Sparkplugs , filters and liquid gadgets from a carton won’t make your car / truck run faster , better , or give you enough change to notice . the diffrence between 300 hp and 320 hp is about less then a mili second and wont do you much good if the car/truck next to you is pushing 400 hp .
I recently proved this to my son in law who has the exact same enigine and truck as i do with his performance chip , KN filter , cold air intake we ended up at the finish line at the exact same time , and he has about 1200 dollars worth after market added crap!

December 27, 2011 at 7:44 am
(231) kc says:

post #213
Mark, since you mention the Viper, everyone should watch the Viper ACR setting the fastest lap time ever in the Nurburgring track in Germany. In particular, watch the gear lever…
Thanks for the throttle explanation.

January 13, 2012 at 9:09 am
(232) Len says:

Your remark about the 6 cylinder being two more hungry cylinders costing you fuel economy is false. Having those two extra cylinders would actually increase your MPG. When an engine can work less to do the same job that saves fuel. Especially since you say your wife always weighs the car down. People think that a smaller engine means better gas milage, when the opposite is true. A personal example is my E-250 with the 4.2 V-6 against the same truck with the 4.6 V-8. The 4.2 gets about 10 mpg, while the 4.6 V-8 is getting better than 15MPG. Same truck, same weight, same driver.

February 2, 2012 at 12:36 pm
(233) Tony says:

Here’s my two cents, for what it’s worth. If performance is what you need, as in racing, go with K&N or something equivalent. Other than that, if you drive a Chevy, use an AC Delco. If you drive a Ford, use a Motorcraft. My point is this: Factory installed products were/are designed for the particular vehicle in which they are installed. Period! All else is pure conjecture. That’s my two cents, take it or leave it.

February 15, 2012 at 3:10 pm
(234) bee watson says:

WOW, i never would have thought something as simple as a air filter would make for such good subject matter. This was the most interesting and entertaining blog i have ever come across, i was therough entertained and enjoyed reading how everyone who contributed to this blog was so passionate in there views and conclussions over what most people wouldnt think twice about .A little old air filter really got people spending there time relentlessly either searching for conclusions or defending there thoughts on the subject. i have to say the majority of the responces were well thought out and persacive in there attempts to solve this great mistery of life?. And congradulations on making something so insugnificant in life as a cars air filter as inspiring to many and entertaining to others as you did . now if we can only harness this passion,effort and enthusiasum and apply it to something a little more meaningfull ,like curing cancer or something of that magnatude. the world would certainly be a better place ,thats for sure. Thanks for the entertainment,

February 18, 2012 at 2:26 am
(235) Mark says:

It is quite amazing that there is so much misimformation , as well as confustion with the topic. No thanks to our goverrment, who actually propagates such myths. If anyone disagrees, look no farther than the EPA who actually endorces the changing of your airfilter to increase fuel economy. Nothing could be further from the truth. If they can get something like this SO wrong what else are they misleading us with?? The reality is, the dirtier theair filter, the less power your car will have when you floor it, which may actually result in better overall gas mileage. This is contrary to popuar opinion, but could not be ore true!

March 1, 2012 at 11:20 pm
(236) Austin says:

After reading this I’ve decided to not buy a k&n filter for my new car. I had one in my 1997 Toyota Forerunner (with a v6), I drove that car until 2003 and recall how dirty it and the inside of the air filter box was when I cleaned it. I wasn’t even sure if I cleaned and oiled it right when I did.

I think having a k&n filter in the Forerunner effected me more psychologically at first. After a month or so, I forgot that it was even installed (that is how awesome it was).

If you are looking to spend some money, customize your car and want a reason, then go for it.. You might as well get it to get some custom seat covers, dice for the rear view mirror, some custom racing stripes, those custom magnetic air-vents for the side fenders, and some custom hubcaps and all the other tacky (custom) accessories that the auto parts store has in stock… Whatever makes you happy :P

March 5, 2012 at 8:13 pm
(237) Joe C says:

This is a very interesting and well covered topic that has gone on for almost 6 years, amazing. After reading just about all the comments from some very intelligent people, I have determined ( or at least believe) that gas mileage does not improve with the addition of a K&N air filter or any air filter for that matter. While it is true that a K&N filter may have a little less air restriction which would probably result in a very small amount of increased HP, you can only get this increase by filtering the air less effectively than oem filters. For what little HP increase a K&N might provide, you pay the price of decreased air filtration. My Infiniti G37 has 328 HP, I am more concerned with better air filtration than I am with increased HP. Mark stated in post 235 that the EPA endorses changing your air filter for improved fuel economy; Mark is correct, the EPA got it totally wrong. A dirty air filter would have had a significant effect on gas mileage in the days of carburetors, but not today; it’s corrected and managed by computers. I’ll stick with OEM.

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