By on April 26, 2019

K&N Panel AIr Filters, Image: OPJosh writes:

Dear Sajeev,

I can remember many times where I’d hear, in passing, someone say that K&Ns and other performance air filters were actually bad for my car… daily or otherwise. Their argument was always that the performance filters allowed that 1 percent of dirt to get through. This argument came up again as Engineering Explained did an air filter . His tests showed a small increase in power at a very minor risk of extra dirt (which seems to be less than 1 percent in many cases).

My question is: If an engine is an air pump and you’re filtering the majority of the dirty out, who cares about the 1 percent that gets through and enters the combustion chamber? When was the last time you heard of an engine dying due to dirty air?

Sajeev answers:

Even in my years monitoring the performance of half-dead hoopties (that often run K&Ns, FWIW) as a 24 Hours of Lemons , I’ve never heard of engine failure via air filtration issues.

Much less seen verification of it!

While the extra 4 hp in a whipplecharged Ford GT (backstory here) is meaningless, the K&Ns had zero adverse effect after thousands of miles. More to the point, considering the reputation and warranty of Underground Racing’s , odds are cotton gauze filters do an adequate job for extreme use… Lemons racing or otherwise.

But what about normal stuff? The K&N (purchased in 1998) for my first Lincoln Mark VIII (reused for my second, 2003 purchase) met my expectations because it:

  • Has 150,000+ collective miles with no signs of wear.
  • Filters almost everything: upon doing a resonator delete in 2010(?), the tube was almost as clean as 
  • Burns zero oil between 8,000-ish mile intervals, no signs of , and has plenty of compression: running hard enough to hang with modern performance cars (until they destroy me with their 6-10 speed gearboxes).

As the tests in the video above suggest, I doubt paper air filters do a significantly better job. But what keeps me a cotton gauze loyalist is:

  • The unbelievably vague promise that meaningful upgrades (computer re-flash, forced induction, etc.) benefit further from that 4-ish HP boost.
  • The “throatier” intake sound, especially after removing intake installed to meet (conformist) consumer expectations and/or possible EPA noise requirements. The latter might be why are a thing, but this mod won’t attract attention if you’re modest with throttle input around pedestrians/law enforcement.
  • Most importantly, they seemingly last forever: comforting for a vehicle that will remain for the life of the owner.

Bonus!  A Piston Slap Nugget of Wisdom!

Let’s talk about a cotton gauze air filter’s oil causing problems with a MAF sensor, which is clearly a sore spot for the manufacturers considering . And if is true, the quote of the “2,500,000 filters K&N sells a year, they encounter less than 200 dealership problems annually” is a good indication that YOU haven’t seen fouled MAF sensors either. 

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

[Image: OP]

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86 Comments on “Piston Slap: An Air Filtration Fallacy?...”


  • avatar
    Lie2me

    I’ve been using a K&N filter in my car since new with no adverse effects, if for no other reason then the cost savings over the life of the car. I thoroughly clean and oil it once a year and am quite happy with the results

    • 0 avatar
      ahintofpepperjack

      Depending on the vehicle it may take 20+ years to actually reach a cost savings. The K&N filter for my truck is $74 + $13 for the cleaning and oiling kit.

      https://www.amazon.com/1796-High-Performance-Replacement-Filter/dp/B0000UUX84
      https://www.amazon.com/99-5000-Aerosol-Recharger-Filter-Service/dp/B00029WYEY

      A paper filter is $13.

      https://www.amazon.com/ECOGARD-XA5090-Premium-Chevrolet-Suburban/dp/B00AKEWRD4

      • 0 avatar
        Lie2me

        Mine was $45 at Walmart and $10 for the kit. Standard filters run about $10-15 for my car, so I’m already ahead. I enjoy maintaining my car and the annual spring cleaning of my filter is one of the things I enjoy. I also think it runs better with the K&N filter. Prior it always sounded like my car was gasping for air, but not with the K&N

    • 0 avatar
      brn

      Not to mention, you just don’t need to mess with it anywhere near as often.

      • 0 avatar
        gtem

        “Not to mention, you just don’t need to mess with it anywhere near as often.”

        How so? If you maintain a K&N “properly,” you’re washing it, drying it, then spraying down with fresh filter oil (careful not to overdo it or you’re contaminate the MAF sensor). With all that hassle and guesswork, I’ll gladly stick to OEM air filters that actually filter better.

        • 0 avatar
          rudiger

          ^This. K&N filters were mostly an expensive boondoggle. Yeah, I can say they improve performance in certain applications. But in smaller engines, they actually hurt performance by robbing low-end torque at the expense of upper-end horsepower. And the one I had on a ’92 Tacoma was noisy as hell. It wasn’t the air intake, but the air cleaner housing wouldn’t silence a metal intake flap that would constantly be opening and closing. It was a lot like the exhaust manifold flap on old Mopars where the spring would break and it would be constantly banging at idle.

          And then there’s the hassle of cleaning the damn things. A whole lot easier to just replace the air filter with a normal OEM unit.

          I used one on a ’94 LT1 Firebird and there was definitely an improvement in the quarter mile) but, drag-racing a V8 Pontiac aside, I’ll never get another.

  • avatar
    -Nate

    Here in the Southwest where even Los Angeles has fine sugar sand in it’s air I’ve seen many worn out engines with K&N filters and the intakes show sand and dirt inside with a simple finger test .

    Worthless garbage .

    -Nate

    • 0 avatar
      Lie2me

      What would you recommend for a dusty environment?

      • 0 avatar
        Jon

        I live in Phoenix and I clean My K&N once a year which is usually about 10-15k. 230k and seems to be working fine.

      • 0 avatar
        JimZ

        a pleated paper air filter.

      • 0 avatar
        -Nate

        “What would you recommend for a dusty environment?”

        Understand that I’m old and worked in dirty & dusty environments before moving to L.A., I like & use oil bath air filters .

        Using ATF instead of engine oil makes them self – cleaning ~ the dust & dirt doesn’t stay in the mesh, it drips down into the oil cup .

        Messy and time consuming to service, I don’t mind .

        Most folks who like Hot Rods will love the intake honk the K&N provides and won’t keep their vehicle long enough to care that engine is worn out in 100,000 miles or less .

        -Nate

    • 0 avatar
      Jon

      Interesting.

      Its been many years since I turned wrenches for a living but I have never seen an engine fail due to a dirty air filter (K&N or otherwise).

      Ive seen a 5.9L Cummins fail to start because of a clogged air filter but started right up after replacement. I have seen paper filters that were extremely dirty and ripped (older high mileage 5.9 Cummins) but the engine was still running without issue (in Phoenix). Ive seen dirty intakes with vehicles that run great – even my 230k GMC had a very mild residue on the inside of the intake when i replaced the throttle body last year; and its had a K&N since 60k (cleaned and serviced regularly).

      I suspect that the gasses introduced via the EGR are far more dangerous to the engines health than dirt that passes through the air filter.

    • 0 avatar
      Flipper35

      When I lived in El Centro (low desert) I never had any dirt past the K&N filter and filter lid on the Cobra replica.

      Keep it clean and oiled and the do fine, and they flow better dirty than paper does dirty.

      Our Durango has over 100k miles on it’s K&N also with good results.

      Let’s not get started on the crap oil filters with cardboard end caps or the new oil spec (SN?) that doesn’t have enough zinc to tun many miles before it needs changed when used in high lift, high load, cam engine because the additive is hard on catalytic converters.

  • avatar
    danio3834

    Spend some time in the world of work trucks and you’ll see all kinds of air filtration related failures. “Dusting” ruining cylinders and turbos galore. Not worth messing around with expensive filters that expose some risk of dusting and offer no real benefit other than a possible long term cost payoff (maybe).

    • 0 avatar
      mason

      Agreed. Oiled filters are particularly detrimental on turbocharged engines, and more so under sustained engine loads.

      Anyone here remember the TSB Dodge released on the CTD engine regarding oiled air filters? It stemmed from an unusually high number of trucks coming in under warranty for dusted engines. Fleetguard did some testing of several aftermarket oiled air filters and came to the conclusion that they did not meet their minimum filtration requirements. This was in the 90’s if I remember correctly. Would be interesting to see how they would compare now.

      • 0 avatar
        Lie2me

        These are all good comments. I have come to the conclusion that the results of different filters vary greatly between different engines and driving conditions. The best bet is to know your car and how you drive it and pick the best filter that works for you

  • avatar
    arach

    I definitely bought an F150 with a CEL for $2500.

    I checked the CEL with my code reader and it said MAF sensor failure. Checked the air filter and noted a well-used K&N.

    Without thinking twice, I bought the car, drove it home, cleaned the MAF sensor with MAF cleaner and got all that K&N air filter oil off of it. I then cleaned the Air filter and re-oiled it.

    CEL gone.

    That was the last time I used a K&N. They cost about $40-50, while regular filters cost about $5 from rock auto. If a regular one is good for 30k miles, then $50 gets me 300k miles. I’ve done 300k miles in precisely 0 of my cars.

    In addition, I don’t have to clean MAF sensors, and re-oiling them is a PITA… much easier just to put a new paper filter in there… the oil kits are like another $10.

    I’ve probably spent $1000 on K&Ns in my life, but no more!

    Then again I’m old and choose convenience > 4 hp any day. K&N just takes too much hassle and time, and solves a problem that no one has.

  • avatar
    JimZ

    It never ceases to amaze me how many people get suckered in by these stupid air filters.

    in 99.9% of the driving you do, the throttle plate is the greatest restriction of airflow by several orders of magnitude. The air filter is upstream of the throttle and isn’t even a fraction of a fraction of a fraction of the total restriction of the intake duct. And even at WOT the throttle body is still the main determining factor in airflow.

    “4 horsepower” is a rounding error. you gain or lose that just due to ambient conditions. just use a standard pleated paper element and change it when it gets dirty.

    • 0 avatar
      SCE to AUX

      ^^ +1.

      Most engines are producing about 15 to 30 HP on the road; nobody is doing 1/4-mile runs all day long.

    • 0 avatar
      MrIcky

      …but then you get a new larger chamfered throttlebody and have your manifold smoothed and polished and a tune and put an airfilter on that you can stick your arm into and you just feel good about the world.

    • 0 avatar
      conundrum

      @Jim Z

      Of course you’re correct. I wrote the same thing in reply to an earlier comment, but canceled it when I read yours. People really have no idea how a gasoline engine works and the giant air restriction a throttle butterfly plate is. Diesel though, with no throttle plate is a slightly different matter but not enough to actually do anything about the air filter.

  • avatar
    incautious

    Biggest problem with any oiled air filter is MAF sensors. Too much oil and the crude will build up fast and they will malfunction. OEM will not warrant a crudded up MAF. Most DYNO results show little to no improvement in HP unless the whole air box is replaced with an free flow box

    • 0 avatar
      Jon

      The issue with fouled MAF sensors is folks over-oiling the filters. Lots of people suspect that if a little bit of oil is a good thing, then a lot of oil must be better. This just isn’t so. Follow the instructions for oiling the filter or use just enough to barely make it damp, not wet.

      One should always wait to start the truck for a few hours after oiling the filter. This will allow droplets of oil to spread into the super thin film the oil is intended to be. I always run a rag over the faces of the filter to pick up any small drops of oil that may have inadvertently formed before i install the filter.

      • 0 avatar
        Lie2me

        You are exactly right, after I LIGHTLY oil my filter I let it sit outside for a few hours turning it occasionally to make sure all the oil is spread evenly

        • 0 avatar
          Flipper35

          I keep a paper one on hand to drive the truck when the cotton one is out to clean and dry and oil and dry.

          These filters make more of a difference on higher horsepower engines. If you get small % more air on a 60hp engine you might get 60.5hp with a filter change. On a 400hp engine for weekend play you might get 410hp. On a race engine or track day car when tenths make a difference they get used a lot.

          That said, cold air will get more for your money.

        • 0 avatar
          gtem

          So a air filter change turns into a Japanese-tea serving style ceremony with careful oiling, turning, etc? :p I’ll just throw a new disposable one in in about 1 minute and move on with life.

    • 0 avatar
      ttacgreg

      At 125 k, my Corolla had to have the MAF replaced due to dust fouling the device. No more brand x air filters for me. I’d get a HEPA filter for it if one was made that fits the car. They are out there for other vehicles but not a 2000 Corolla.

      • 0 avatar
        -Nate

        Yabbut ;

        You won’t be _COOL!_ .

        I think it’s the louder intake honk that makes most like these .

        The hot under hood air is a real thing for those interested in facts and reality .

        -Nate

  • avatar
    ajla

    Don’t the higher trim (like Shelby and 392 Shaker) versions of the Mustang/Challenger/Camaro come with open-element cotton filters from the factory?

    I don’t know if that’s due to actual performance gains or just aesthetics, but if they were reliability nightmares I doubt the manufacturers would be using them.

  • avatar
    87 Morgan

    this is a very interesting thread. I think that some engines respond better to a K&N style cold air intake then others. I have had K&N (ish as their are other brands that do the same thing) in several cars and did not notice a difference. However, the 5.3 in my Suburban had a noticeable improvement when I removed the massive airbox. So much so, I have been considering (for about 1.5 years, I tend to move slow on some things) removing the factory exhaust after the cat and adding a Gibson. Helped my neighbor and it did wonders for his Sierra 6.0. The factory exhaust/muffler is about the size of a 50 gallon oil drum. Near as I can the the GM LS motors like to move a lot of air, in and out, remove as many of the restrictions as possible.

    K&N in my Cummins? Had it for a couple years and removed it. As noted, total PITA did nothing other than need cleaned every 2k miles or so. It was really frustrating.

  • avatar
    indi500fan

    It’s all about the environment.

    I had a buddy back in Cleveland (wet climate) who ran a 283 Chevy over 100,000 miles with no air filter at all, just that old Rochester 2GC hanging in the air.

    I’ve seen pickup trucks run on Arizona desert testing with a lot of grit downstream of a K&N…in that environment they’re probably not the best.

    Outfits like K&N and some specialty oil companies spend a lot of money advertising in buff books and websites, so you’re not going to see them get criticized very often.

  • avatar
    TR4

    Back in the day before positive crankcase ventilation (PCV) the normal filter was oil wetted (much like K&Ns). The better choice was an oil bath filter, which added a pool of oil at the bottom, where the airflow reversing threw off dirt particles into the oil. Some say the oil bath is still the best for very dusty conditions.

    When PCV became standard in the early 1960s the paper filter also became the norm. Much cheaper, easier to service, and because of PCV it would not clog up with the oil mist from the breather cap.

  • avatar
    JMII

    I’ve run K&N filters for years with no issues on both a Dodge and VW to over 100K miles. Granted I live in FL where humidity is a bigger issue then dust. Once a year I clean and re-oil them.

    Like many OEM serviceable parts the factory paper filters seem to be made as cheaply as possible in an effort to save another penny. So is the K&N over priced or is the OEM part just cheap junk? For the cost of a tank of gas I’m not going broke buying one K&N filter per vehicle.

    • 0 avatar
      JimZ

      what, exactly, is wrong with the factory pleated filter? have any of them failed on you? or are you assuming they can’t be any good and thus you need to buy a tiger-repelling rock (K&N?)

      this is like those people who religiously use some pointless “miracle” oil additive and then boast about how “it’s gone 150,000 perfect miles on this and I swear by it.” Ask for any evidence their engine *wouldn’t* have gone 150,000 perfect miles on just the factory recommended oil? crickets.

      • 0 avatar
        Lie2me

        On my car the standard OEM filter didn’t seem like it let enough air through. After changing to K&N it seems to breath better. Just my personal impression

        • 0 avatar
          JimZ

          Lots of people believe dumb things based on their “personal impression.”

          I highly doubt your “personal impression” is based on anything other than looking at the filters and jumping to conclusions.

          • 0 avatar
            Lie2me

            You’re wrong, the “personal impression” I was referring to was how the car ran, with the K&N the engine seems to get more air and is able to run better. It has nothing to do with “looking at the filter”

        • 0 avatar
          ravenuer

          Did you do any air flow tests to base your impression on?
          Come to think of it, my car just seems to run better after I wash it.

          • 0 avatar
            pwrwrench

            I read about a guy that raced small sailboats. He had a routine hull cleaning method to reduce water drag, but then he coated the hull with a mixture that included egg whites. He was sure that the boat went faster!

          • 0 avatar
            Lie2me

            Look, we’re talking about a filter it’s not rocket science, if I think my car runs better with the K&N that’s what I’m going to use

          • 0 avatar
            -Nate

            @ L2M :

            There’s little doubt that you feel more power, anything that increases air flow will give at the very least better throttle response, the issue here is does it filter as well and no, it doesn’t .

            Enjoy the ride and don’t worry about it .

            -Nate

          • 0 avatar
            JimZ

            “if I think vaccines cause autism then I’m not getting my kids vaccinated! Who needs evidence?”

            “if I think those are chemtrails streaking across the sky, that’s what I’m going to tell people! Who needs evidence?”

            yes, it’s not rocket science. that’s why pleated paper filters have worked fine for decades.

            god, I hate how this country encourages people to go with their “gut feeling” no matter how dumb it is. Asimov was right when he said we have a cult of ignorance in this country, and let people think “my ignorance is as good as your knowledge.”

          • 0 avatar
            Lie2me

            Oh c’mon, you’re comparing an engine filter with your kid’s health?

          • 0 avatar
            JimZ

            No, but it’s the same mindset. Believe in something which “sounds right,” without caring whether or not it IS right.

            people make a snap judgement based on nothing, and disregard mountains of evidence to the contrary.

            https://www.psychologytoday.com/us/blog/true-believers/201603/5-reasons-why-people-stick-their-beliefs-no-matter-what

  • avatar
    DenverMike

    Isn’t there a “downside” to every performance mod? As far as “bang for your buck” goes, K&Ns are still near the top of the list.

    It’s only when automaker get it “wrong” or have concerns that overrule performance, and that’s where mods can have no “downsides”, like “silencer boxes”, ahead of air filters on Fox Mustang 5.0s.

    Ring & Pinion (gear) swaps “limited slip” (if your car or truck didn’t come with it) are awesome “bang for your buck” mods or upgrades, that may have no “downsides” or ill effects, depending on your driving situation and original equipment (specs), meaning the OEM was a little too concerned with fuel economy and or cost cutting.

  • avatar
    TR4

    Has anyone tried combining a K&N filter with a Turbonator?

    • 0 avatar
      JimZ

      yes. when I had my Mustang I had a K&N air filter with a cold air intake (drawing air from underhood, natch,) a fuel ionizer, Tornado Air vortex generator, Pulstar spark plugs, fuel line magnets, and a 00-gauge ground strap kit. after all that it had 650 horsepower and actually *made its own gas.*

  • avatar
    S197GT

    According to K&N all this MAF talk is false. From a 2006 article on their website:

    “If a mechanic or dealership claims excess oil from a K&N Engineering Lifetime Air Filter caused a Mass Air Flow sensor (MAF) failure, it’s not true. K&N has researched, tested and devoted many hours to confirm the use of K&N Air Filters, including over oiled air filters, will not cause a Mass Air Flow sensor failure under any remotely normal driving conditions.”

    “Oil does not come off K&N Filters. If a mechanic or dealership claims K&N is the problem there has to be proof. ”

    “In a period where K&N sold more than 5 million filters, 52 sensors were evaluated. Not one of these suspected MAF sensors sent in for laboratory evaluation were shown to have failed because of contamination from K&N filter oil. In fact, 28 sensors were in perfect operating condition. K&N helped those consumers recover money for unnecessary parts and labor.

    The other 24 sensors failed due to factors not related to K&N. There were traces of silicone potting compound which is used in the manufacturing process of MAF sensors, meaning the MAF sensor contaminated itself. There was also evidence of motor oil contamination from blow-by; a condition where oil vapor from combustion is re-circulated into the vehicle’s intake tract.”

    “K&N encounters less than 200 dealership problems annually, which is very small compared to the number of filters we sell annually (2,500,000), and we treat each situation as if it were our own personal problem.”

    Facts be damned… old people gonna hold onto their old wives tales. Technology never progresses, things should always stay the same, get off my lawn!

    • 0 avatar
      JimZ

      according to K&N, K&N is awesome.

      Good to know.

      • 0 avatar
        ravenuer

        LOL! And I bet K&N got all their facts on them interwebs. And you know what they say about stuff that’s on them interwebs….

      • 0 avatar
        Prove your humanity: 9 + 8 =

        Then there’s the obvious fallacy of it being a “cold air intake”. Hot air under the hood (heated by the radiator and the engine) is at a much higher temperature than air ducted in from behind the fender.

        K&N should advertise how the much warmer air in the vecinity of the exhaust manifold somehow vaporized gasoline better.

    • 0 avatar
      Scoutdude

      Fact is I’ve seen many contaminated MAFs from cars that used nothing but paper filters.

      My 03 Mountaineer has had a K&N filter since day 2 and have never had a single problem with the MAF in 160k miles. Of course I follow the directions and do not service it every year like some people.

  • avatar
    pwrwrench

    And how many everyday drivers are going to recognize a problem caused by an air filter and take the time to notify the manufacturer?
    I’m with Nate on the air filters. With one difference change “worthless” to expensive, compared to ‘stock’ air filters.
    When I started racing cars, in the 1970s, it was off-road desert. Air filtration is very important to finish a race. A race team got sponsored by K & N, but had engine problems that the engine builder found to be caused by dirt, dust and silt wearing the rings, pistons, and bearings. There was a lot less HP after 400 miles and oil was coming out of the crankcase breather due to ring/cylinder leakage. A testing lab was consulted and tests were run on various air filters. The K & N would let fine silt through as opposed to a “paper” filter. So to keep the sponsor deal an oiled foam filter was put inside the K & N. This solved most problems.
    Later most off-road racers adopted the centrifugal filter from earthmoving equipment (tractors, dozers, etc). In this design the air swirls as it flows through the filter housing and much of the dirt and dust is caught in a rubber flapper valve before it can get to the large paper filter. When the engine slows down there is still flow through the filter and the flapper opens pushing most of the dust out. This allows longer use between servicing/replacement.
    I knew someone who ran an auto parts warehouse in the 1980s and 90s. The business moved from L A to Las Vegas. His son told me, “We sell a hell of a lot more air filters” due to the frequent dust storms.
    So it’s very condition dependent. If you are in a dusty area, check/replace your air filter more often.
    I have seen problems with K & N often due to lack of or improper maintenance. Too much or too little oil, and improper cleaning. The rubber around the edge of the filter can harden or shrink letting dirt into the engine.
    I bought a K & N once, it did not fit properly and consulting K & N did not offer any effective solution.
    Bottom line, in more than 30 years in the auto repair business, it will cost a vehicle operator more by failing to service things properly. Dirty oil, air, and fuel filters lead to expensive repairs and breakdowns.
    There is a lot more to air filtration, but this is long enough.

  • avatar
    eggsalad

    Not a fan of their intake air filters, but has anyone tried their cabin air filters? I change the CAF far more often than the intake filter, and the financial payback of a washable CAF is just a couple years.

    I’m tempted. Besides, nothing’s gonna fail if your CAF is no good.

  • avatar
    cimarron typeR

    I’ve used K&N indirectly as part of 2 aftermarket supercharger kits when I had BMWs. No issues with MAF failure.I put a pair on my G37S when a poster noted better gas mileage. I did gain 1mpg highway MPGs improvement, and a slightly better throttle response but no real power on butt dyno (mines a Mustang not dynojet). There was an online sale for 60.00 free shipping for the pair, I thought i’d save also on tax, turns out the warehouse was here in KC, go figure.
    We have pretty much no dust here in suburbia so I doubt I even needed to clean every 20k, if that.

    Honestly , I wouldn’t change a cabin filter unless it smelled funny in the car. It’s just a dealer cash machine to include in the annual service.

    • 0 avatar
      pwrwrench

      Funny, about cabin air filters. A co-worker bought a base model ‘something’ (don’t recall what). When it came time to change the filter he found a plastic frame with lattice instead of a filter. The filter he got at the FLAPS fit exactly in place of the plastic thingy. A $ buck or 2 for XXX K cars built = a lot of money for the car company, but little cabin filtration for the drivers.

      • 0 avatar
        Cactuar

        Same thing I found on my 06 Odyssey LX (base model). The tray for the filter was indeed in the glove box, but there was plastic webbing on the inside to prevent a filter from being inserted. I just removed it with a knife and installed a filter.

        It’s amazing that Honda would even bother to stock two filter trays. Obviously a push from the marketing team so they can add one more bullet point to the EX model.

        • 0 avatar
          EGSE

          The ’02 F-150 had an optional cabin air filter; the used one I bought didn’t come with one so I bought one and…like the Odyssey, the slot for the filter was blocked. The filter slot is so close to the floor that it’s very difficult to saw the obstruction away. Maybe someday I’ll get it done….

  • avatar
    NeilM

    I use an ITG multilayer foam filter in my M3 track car. ITG’s oil comes in an aerosol can, and once its solvent evaporates the remaining oil is extremely tacky and definitely isn’t going anywhere. I wouldn’t use any kind of oiled filter where the oil is liquid enough that you have to turn the filter to distribute it evenly, e.g. K&N. That’s a recipe for oil particles to contaminate the MAF sensor element. The ITG filter easily passes the “white glove test” of wiping inside the intake tract to detect dust.

    But for street driving nothing beats a decent stock paper filter, particularly because the pleats give it a huge surface area. They’re also cheap and easy to replace.

    There are standardized tests for automotive air filter effectiveness, e.g. the Arizona Road dust test. (You can even buy ISO/SAE/etc. standard “Arizona Dust” for the purpose, see https://www.reade.com/products/arizona-test-dust-ansi-ard-arizona-ashrae-iso-jis-mtd-nfpa-nist-rm-srm-sae.)

    The worst problem with filters/intakes are the many poorly designed aftermarket air intakes which actually inhale hot air from the engine compartment. Factory intakes, and the better aftermarket units, always have an outside cold air source.

  • avatar
    NeilM

    Well, colder than the engine compartment, anyway!

  • avatar
    Carrera

    When I bought my 2007 Ridgeline with 9k miles on it, it came with a K&N filter installed. I always drove that car in an environment that wasn’t too dusty so I didn’t lose too much sleep. I did clean it as per the instructions when the car had about 45,000 miles on it. Cleaned it then oiled it lightly and I let it dry for 12-15 hours. In the meantime I used a regular Fram. I’ve never had an oil analysis done but if you are to follow Bob is The Oil Guy, most guys who used the filters and do oil analysis report a high number for silicone. Is that worrisome? I don’t know. Would I pay 49 dollars for one? Probably not. I am a good candidate for one now since I drive 30,000 miles/year in my Corolla but stock Denso are cheap enough.
    Depending on driving conditions I would not clean them too often. If one is to believe Bob is The Oil Guy, a filter when is reasonably dirty, protects the best so by that logic, a K&N protects best when is a bit dirty.

    • 0 avatar
      mason

      Silicone is an indication of dirt passing through the filter but there are other possibilities. If one uses oil additives there can be anti foaming agents containing high levels of silicone. A freshly rebuilt engine or one that has just been resealed can also show elevated levels of silicone in a UOA.

      And it is true that a dirty filter will provide better filtration as it collects dirt. This is true regardless of filter media. Over servicing is a real thing, especially with heavy equipment or vehicles driven in dirty environments. Each time a filter box is opened up increases potential contamination of the clean side of the intake. These are the reasons why you see filter restriction gauges on big trucks and heavy equipment. Part of it is the cost of the filters but mainly because they don’t want you touching it until it needs changed. External inspections only.

  • avatar
    Jagboi

    I knew a guy who ran a race team, and about 10 years ago he did an experiment. At the beginning of the race year he prepared two identical engines, and measured and kept records of all the engine specs. One engine went into a car with a paper air filter, and the other a K&N.

    As much as possible the two cars were driven the same, they competed at the same races. Neither of them seemed to have an advantage performance wise, the lap times were within margins of error and driver style.

    At the end of the season the engines were torn down and measured again. The engine with the K&N had measurably more bore wear than the paper filtered engine. In his opinion the K&N only kept out “boulders”, and he stuck to paper filters after that.

  • avatar
    ToddAtlasF1

    I don’t have a strong opinion on whether or not K&N filters work. There are racing series where they try to optimize molecules that use K&N filters, so at the very least they flow well. I had one in one of my cars back when I thought such things might matter. I couldn’t detect a performance difference, nor could I really detect a difference from a Dinan chip, etc… I recently ran a shop, and the funny thing about K&N filters is that some people who buy them pay for shops to ‘recharge’ them. It is a pretty labor intensive process at a hundred dollars an hour or so. Figure three tenths of an hour to pull the filter out and put it back. Figure three tenths to spray the cleaning chemical on the filter and rinse it out. Figure two tenths to retreat the filter after it dries, which takes forever and means you’ll be charged to bringing the car or truck in to a bay twice. The kit to ‘recharge’ the filter is going to set you back $20 or so bucks at shop rates. You’d be much better off financially to order a new K&N and drop it in yourself if you don’t have the time to clean and re-oil your filter.

  • avatar
    Rengaw

    I’ve got a 2009 RAV4 with 122,000 miles. In the 10 years I have owned the car I have never cleaned the MAF. I live a mile into a really dusty road. I change out air filters once a year and use the OEM type filters.
    Yesterday I decided to clean the MAF. I was shocked the MAF was clean as a whistle. And after I spray cleaned it, it looked no different than when I started.
    Anyway, it left me totally impressed at how great the regular OEM filters were doing their job.

  • avatar
    Jeff S

    I use AEM dry filters on my S-10 and Isuzu. Maybe they are not any better than the throw away filters but I figure as long as I keep my vehicles it does not cost that much more. And yes I add fuel additive every once in a while but I see it as an ounce of prevention.

  • avatar
    jeffmete

    Generally the auto engineers don’t get it wrong on filter design, but they do have to protect for the worst case customer who lives 30 miles back on a talc road. Most people who drive on paved roads can get by with a lot less filter robustness. Spent my career at Cummins and saw plenty of dusted out engines. Most because the filters would get too dirty and partially collapse some where along the intake letting in dirt. Cummins actually made a movie back in the 60s to show our customers the importance of maintaining the air filter. Started out with good looking engineers all sitting around smoking at their desks.

  • avatar
    Jeff S

    Agree most of the roads I drive on are paved but years ago I did live on a farm with a gravel road and changed my air filters once a year which is still not that bad. Seems the old round filters with the carburetors would require replacement more often.

  • avatar
    dantes_inferno

    After using K&N filters for years, I made the switch to AEM Dryflow filters. No more oiling – all you do is wash (with air filter cleaner), rinse and dry. Comparing the two reveals that the AEM feels more solidly constructed (especially the seal) than the K&N.

  • avatar
    don1967

    I’ve got three-quarters of a $20 cleaning kit left over from the $90 filter I justed traded away in my previous motorcycle, for anyone who wants to “save money” like I did.

    Let’s face it, the real purpose of a K&N filter is to give yourself an excuse to spend more time in the garage.


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