Mod Edit: This is a 9 year thread bump, most of the people prior to this thread haven't logged on in years. Many links may be broken.

It's often been said here by disbelievers of K&N's marketing claims that K&N filters don't filter very well, that they let a lot more dust through and into your engine. There have been cursory studies that didn't stand up to scientific scrutiny of the rigorousness of the methods, but here's one that was performed exactly according to the ISO 5011 Standard (formerly SAE J726) air filter test cycle. The filters tested were for a GM Duramax diesel engine, but it was the filters that were tested - and the conclusions are valid for all filters of similar materials (ie, a K&N filter in a different size still sucks at filtering).

Here's the test, with write-ups, raw data, and analysis: ISO 5011 Duramax Air Filter Test Report.

The data is all there. The K&N lets through more dust than any other filter, yet clogs with dust/dirt and gets restricted sooner than any other filter (at the same time as letting more dust/dirt through - an amazing trick of incredible incompetent design!). There is no other way to interpret the results, and the strict adherence to the controlled test procedure eliminates the usual arguments against such test results.

This is solid, incontrovertible proof that K&N filters are extremely poor filters, and any benefits claimed are bogus, false marketing claims. What good is using a filter that might flow a bit more air (when the air filter isn't a restriction anyway, so they don't make any more power) but that lets through a lot more dirt? The whole point of a filter is to keep as much dirt out as possible, to prevent wear and damage to the engine! K&N users, Is the improved (louder) sound really worth the damage you're doing to your engine????

Regards,
Gordon

 

The one potential problem I could see with the K&N and other oil/guaze filters is that the oil can contaminate the "post filter" and make it weigh more which would show up on the test as decreased filtering efficiency since they are basically looking at the mass of dust going in and the mass gain of the post filter.

I didn't see it mentioned in the write up, but normally in a test like this they would heat the post filter up to evaporate any moisture from the air, but the oil probably would not evaporate too much.

 

So their filters suck their typhoon intake sucks -- I guess K&N must be made up of a bunch of suckwads.

 

Makes me wonder why K&N is a "brand name" to so many.

 

I've read somewhere that the worse filters you can ever put on a car are the "sponge" type which many Jap aftermarket companies come up with.

I'm referring to the HKS and Greddy types which don't "filter" out dirt particles as well as K&N and allow basically everything bar larger pebbles through.

K&N may not be as efficient as the OEM stuff, but hell, I don't think they're the worst on the market.

Just my 0.02c.

 

Because they see the name on TV..

I see a new one from FRAM calling the filter "Air Hogs'

If an air filter suddenly gained 5 hp, don't you think it would be the one that Mz used in the first place?

 

No because it would be a trade off between engine longevity and power.
I'm sure they wouldn't want too many warranty claims on their hands.

Interestingly, the S2K has a cone shaped paper filter located in the standard airbox, I'm curious whether its the actual filter size/shape not the filter material which gives the power gain. Anyone know this?

 

Isn't the RB intake going to come with a K&N?

 

It's coming out with a cone shaped filter, not 100% sure if it definitely will be a K&N one.

But being enclosed, yes it will still allow dirt through, but not as much as an "open element".

 

Yes Gordon, but one swallow does not a summer make...! Taken at face value, the results of this test look bad for K&N, but this test was not statistically significant. I mean, they tested a sample of one!

If K&N sell 1000 filters and their quality control lets 2 dodgy ones through for public sale, they have 998 good ones out there....and 99.8 percent of their filters perform faultlessly. If our friend tested one of the 2 dodgy ones, he is going to come up with bogus results.

K&N report on their website that they regularly carry out the same test, with independant testers, and their filters trap 97 to 99% of the "test dust".

Without testing of further samples, we can only draw the conclusion that a SINGLE K&N filter failed to perform as advertised. I don't have a K&N and I'm not defending them, but the maths is bad. You really can't draw a statistically significant result from this test.

Gomez.

 

I wouldn't be too quick to throw the baby out with the bath water. Aside from looking like a Delco commercial, the differences aren't all that discouraging. The stated filter efficiency from best to worse is 99.93% to 96.08% or only 3.85%. Statements like 39% more efficient are totally subjective since they don't give a base-line to establish how they arrive at their number, so it's just a statement, not a fact.

To put this in perspective, take a close look at the particle size distribution of the test dust. A micron is one-millionth of a meter, or 0.000039 inches. So 89.1% of the particals in the test are below 80 microns or 0.00312 inches (that's 31.2 ten-thousandths of an inch) and the data shows the remaining 10.9% only as over 80 microns.

Some relationships you may recognize for reference are:
Grain of coarse sand = 500+ microns
table salt = 100+ microns
Human hair diameter = 80-90 microns
Smallets partical visible to human eye = 50 Microns
Airborne pollen = 30 microns
Typical Municipal filtered water = 10 microns
Talcum powder = 10 microns

They didn't use the fine test dust in any test, and even state that the coarse dust was used to provide higher filter efficiencies; when everyday driving is more likely to encounter particals closer to the fine dust specification listed. Nor did they run any final filter tests with no filter installed to establish ambient air particulate loading or baseline test system head curve.

So the question should be "what does all of this mean in everyday use?" In my opinion, it means that all the filters tested are pretty damn good, and will do a good job protecting your engine internals. When I read Gordon's thread title, I expected to see something of greater consequence. I think we're still where you pay your money and take your choice.

 

Yes it is. While their at their open house, Jim said that it was a specially designed K&N filter just for them.

 

If K&N filters are so universally crappy, why do so many race teams use them? Sure, they're probably getting sponsorship money, but given that if they don't perform well as a team, that hurts their business, I can't see them using these filters if they're so bad. Now, the usual counter is that they flow better, but they don't filter as well, so its OK for a race team that will be rebuilding its motor anyway, but not for a street car...but this seems to be saying they flow poorly as well. Somehow, it all doesn't really add up.

jds

 

they don't use any filters, because they don't flow as well as an unrestricted velocity stack. also, the name is on their car because of money, no reason other than that.

being a scientifically controlled test, you can't so easily refute what this man has put together here. people want to know, what's the best? what's the worst? why?
some of what has been done here has answered that, which is basically that paper media filters do not hinder airflow nearly as much as most would have you believe with pressure gradients found during the performance of your usual street engine, and that they obviously filter a whole lot better than filters composed of a lower density matrix (like the plastic type K&N employs).

it's not a complicated thing, i don't understand some of the hostility.

 

Please understand that Gordon has always hated K&N filters and will go far out of his way to prove his point. He does it every chance he gets. He doesn't like them and that is his right. It is just an opinion as far as I am concerned. I have always use K&N and have never had a single problem with them. Racing Beat endorses them. Paul Yaw the true god of all things rotary uses them and he is probably more results and fact driven than anyone. Things that are abrasive enough to destroy your engine internally are far bigger than a micron. There are alot of K&N style filters out there that look the same but don't perform the same. Many of them are crap. If we see a test between several filters and the test includes extremely fine particulate matter of a micron or less and the worst filter is still above 95% efficient, that is pretty damn good. Gordon makes it out like the K&N are only 75% efficient and you are going to destroy your engine if you use one. Nothing and I stress nothing, can be farther from the truth.

I don't know how well that test in that article was run but it is a proven fact that the K&N filters flow more in a clogged state than paper filters do. The rebuttal to this is almost always because it doesn't filter as good. So basically we are saying that the matter most responsible for clogging air filters is less than 1 micron in size? Um, no. Anything that small short of a diamond will not do anything to the engine. There is nothing hard that is that small. At lest nothing that will get in your engine. What about the carbon buildup inside an engine. You can see it and it is known to chip off. Yes it is soft. So is everything small enough to pass through an air filter.

Baja off road racers and other race teams use K&N. The rebuttal to this is that they usually rebuild their engines so they don't care. Bullshit! They need their engines to run at full power for as long as possible. The ones who don't care are the ones who use no filter at all. Take a look at drag racing. They do rebuild their engines often. The Star Mazda cars use K&N cone filters too!

This above test proves absolutely nothing beneficial in real world applications. There comes a point where nit picking doesn't do anything anymore. Paper filters don't flow as well. Do they filter better? Maybe. But they don't stop anymore harmful particulate matter than a K&N. Anything that small is not much to worry about. The oil that your oil metering system is injecting into the engine is putting far larger and harmful things into the engine than a K&N filter is. If you can see metal shavings or a silver sledge in your oil, these shavings are also getting into your engine through the omp! Oh yeah, no one remembered that!

And you guys are nitpicking over an air filter? Sheesh!

 

RG, there is only one person in this thread who is nitpicking.......and his name is at the top .

 

well, it isn't only that they don't filter fine particulate as well, but also that they (at first blush) take more energy to move air through them, and plug up faster according to the testing this guy has done.

 

Maybe I should stay out of this, it's starting to look like another Canada vs USA thread .

 

heh, i don't care :D i just hate rice-o-modders who throw in a filter and think suddenly they have an extra 15 hp to the wheels because paper filters are horrendous or something. cheering for the underdog is fun.

 

I find this all pretty funny because the only motor I have ever heard of needing a rebuild from an air filter was one a turbocharged car that had a greddy foam filter that was really old and the foam was breaking away and got sucked in by the turbo. I think its hilarious that you would believe a difference of 98% and 96% efficiency of filtering particles smaller than the naked eye can see will significantly reduce the performance and life of your engine.

 

I don't "hate" them, and haven't always - in fact, I have owned K&N filters in the past. However, that test I linked is no opinion - it's the most scientific, controlled air filter test I've yet seen, and the FACT is that the K&N filter performed very poorly. (To the suggestion that they simply got a bad filter - no, I've seen quite a few less well controlled tests that gave similar results with the K&N filter filtering less effectively)

What I don't like is bullshit marketing claims, and in that regard K&N is one of the leaders of the pack, just behind Splitfire and Slik50!

The point is that the K&N was next to the worst filter of the bunch. NOT the best by any means, which is what K&N claims. As far as filtering goes, 95% isn't bad - but when your OEM filter actually does a better job of filtering, then it isn't great either. After all, filtering is what those things are supposed to do, right? And there are a LOT of better filters out there. What's the big deal with K&N filters then, when they are certainly no better than the other alternatives?

That test was run by a professional independent lab according to the ISO 5011 test procedure. Hard to argue with that or complain that the test wasn't conducted correctly, isn't it? As for the "proven fact" - actually, the results of that test showed that the K&N clogged sooner than the paper filters they tested, even though it also passed more dirt. An amazing feat, as I mentioned! All the data is there, just go look at it. That test just disproved the "proven fact" that K&N claims. PS - they did test the K&N with both coarse and fine dust - the K&N clogged even faster with the fine dust.

Real world? Let's consider - in the real world of street cars, the air filter is NOT a restriction that is costing horsepower. Take out the filter completely, and an RX-8 will not dyno more than 1 HP higher. Put in a K&N, and it doesn't make any more HP. Who cares that it can theoretically flow more air, when any paper filter can flow as much air as the engine needs??? Real world, a K&N doesn't provide any more HP. Even changing out the stock panel filter to a K&N cone filter does NOT provide any more power - look at all the tests and experiences on this board for proof of that fact in the RX-8 street world. The nit-picking is to insist that the K&N flows better, when THAT DOESN'T MAKE ANY DIFFERENCE! So what? That's as relevant as to insist that it's red instead of white, and red is better. In the real world, the colour of the air filter doesn't matter.

So we have two major requirements for an air filter - flow capacity, and filtering dirt out. We know that flow capacity is NOT an issue, as all of them will perform the same on our street application. Therefore, the difference between air filters comes down to their filtering capability - and this test (along with pretty much every other independent test I've seen) proves that K&N filters do NOT filter as well. Tell me again why I'd ever want to spend extra dollars for an inferior filter?

Racers? Come on, what a lame argument. Their filter requirements are much different than street filtering requirements, and you certainly understand the engineering analysis of requirements that goes in to selecting a race air filter will be much different than the requirements for selecting a street filter. If you insist, I can list them, but you actually cover a bunch of them yourself. Yes, in race use, ultimate flow capacity will be a much bigger factor, and engine durability in the hundreds of thousands of miles range will not. I would never base oil selection for a street car based on what Ferrari runs in their Formula1 engines, either, because their requirements are much different than mine (That also points out that the use of Redline in race engines isn't really a great recommendation that Redline is the best oil for street use, for example. I'm NOT saying anything against Redline, please note, just pointing out that products that are great on race applications aren't necessarily great on street applications, because of the vastly different requirements).


I don't know about you, but I run an oil filter on my engines. The best one that I can find, for that matter - in terms of its filtering capability.

However, if you're familiar with oil analysis, then you know that oil analysis actually shows the differences between air filters. I've seen several tests where people find that silicate content in oil increases when they run K&N filters. Why? Because the K&N filters are letting more particulates (ie fine particles of sand, composed of silica) through into the engine. Yeah, your oil pumps stuff around the engine that can cause wear - your argument about the oil, then, is actually another argument AGAINST using K&N filters.


Nitpicking? How many people here discuss and debate the best oil filter for their engine? The best oil? People want to know what products will provide for the longest life and will do the best job preventing wear. Air filter choice obviously contributes to that as well - and it is NOT nit-picky to want people to know that some filters protect better than others (especially when those others do NOT provide ANY benefits beyond noise in our specific application), despite the marketing department's claims. I don't buy the hype for Splitfire plugs, Nology plug wires, Slik50, and I don't buy the hype for K&N. That doesn't mean I hate them, by any means - for different engineering requirements (where long life of componentry is not a primary concern), then obviously my criteria would be different and a K&N filter could be an excellent choice. Not ever (not ever again, that is) in one of my street cars, however! :D

Regards,
Gordon

 

While you and I have had our differences in the past (over on Miata.net), I'm with you 100% on this one, Gord. K+N filters give people a "sound", and that's it. Their marketing team has done a great job convincing the public that they do more. If you want to improve on a stock intake, then look to diameter, length, location of the MAF, etc., but leave the paper there.

There are some aftermarket drop-ins that are paper as well, but offer more pleats (thus, more surface area) that may be an improvement, but after cleaning all the oily crap out of the TB and intake manifold of my Miata, I'm not a big K+N fan. This test just gives one more reason.

 

First of all, Gordon I do respect you and in no way am I trying to flame you for this thread. Please don't take it like that. I do agree with Gordon in that filters are not going to give you more power. Especially not on the RX-8. The key to gaining power is in the airbox design, not the filter. I do agree that people shouldn't go out an buy new filters because they think they are going to gain power.

I do think that the filtering ability down at the micron level and which style gets extremely fine matter is irrelevant once you get to a certain point. I believe this point is above where both paper and the K&N filter to. Things that are small enough to pass through a K&N filter but not a paper filter are not large enough to cause harm. The fact of the matter is that no one has any proof that any filter has ever caused any engine damage by virtue of it's filtering ability. Filter construction on the other hand is another matter altogether. Some filters just aren't built worth a damn and will fall apart. That may be cause for concern about using other filters but the K&N are durable. The biggest mistake people make with these types of filters is during cleaning. Never use an air hose and blow through them. Do not use a high pressure water hose. Both methods will put holes large enough to be seen with the naked eye through the filter element. That is bad news and now the filter is not working good. The biggest single advantage that filters like K&N have is that they can be cleaned and reused. The argument against this is that paper costs less and offsets this. OK, fine.

Lab tests are all fine and dandy but they aren't under real world conditions. I'd like to see someone use a paper filter element, establish a base flow, drive it for a 5 thousand miles and then remove it and test it's flow restriction again. Then I'd like to see the same done with others. This is alot of mileage but I think it is more realistic in it's outcome. In a lab, you may be in a controlled environment, but throwing a measured amount of dirt at something and then measuring the results isn't realistic. There is no better test than real world use. That's what I consider to be significant. If I remove my air filter and run my finger along the inside of the intake tube, it is still clean. I have never once gotten dust or dirt when using a filter paper, K&N or otherwise. I still going to use K&N until I see a real condition test that proves otherwise. There have been many tests that showed they worked good but 1 test differently is proof? I want real world results, not lab rat tests.

 

I'd just like to reiterate my point that a false low efficiency number could purely be from excess oil (these were new filters tested) getting on the post filter. Its not hard to imagine that 1-2 grams of oil could have come out of a brand new K&N - after all there is a TSB out there for oil contaminating MAF's.

I would just find it strange that the filter thats accused of leaving the most dirt through would be the first to clog up - usually in the filter world the filter that has a finer capability and more efficient media plugs up faster then a filter that leaves more of the dirt go through.

 

Yeah. I put a Weapon R intake on my dad's '84 318i and it looked like plastic gauze. I could see through it no problem. I don't know how it could possible trap any dirt.

As for the K&N, I don't think that the extra dirt they let through is enough to hurt a motor, nor do I think that they don't produce and power. If this claims were true, the brand wouldn't have lasted this long and built up such a reputable name for iteslf.