The right way to filter air

K&N Air Filters--Snake Oil Soaked Cotton Gauze
December 2004

OK, this is going to be long, and I apologise for that--stop reading here if you have a "faith-based" fundamentalist and unshakeable belief in K&N filters, you will not like what I have to say.

Having participated in a number of these discussions and having reviewed K&N's website, and after review  of numerous test reports and anecdotal sources available on the web I have come to the following conclusions and associated statements of opinion.
1. K&N drop-in filters, when new and/or properly maintained, may provide increased air flow as compared to a paper OEM style filter--however, at best any gain they provide to modern smaller displacement vehicles is trivial and it comes at the expense of inferior filtration.

In fact, K&N (per their website) makes no claim that they do. They state: "We design our air filters to provide minimum restriction allowing high airflow into an engine."--however, there's nothing here that claims that others don't.

They then state: "Because no two air filters are alike, the specific airflow and overall filtration efficiency will vary depending on the filter in question. However, you can rest assured that each air filter we sell, has been designed to achieve high air flow while providing superior filtration."--there's more fudge in this sentence than in all of Helen Georgia (if you've been there you know what I'm talking about).  "Efficiency will vary", "has been designed to..." (but does it really?), "providing superior filtration" (superior to what?).  I couldn't find any unambiguous, unqualified, explicit claims of higher air flow and superior filtration used in the same sentence in any document on their site.

A claim of doubtful empirical implication is: "Tests performed by an independent laboratory commonly known as the Frazier Permeability Test have shown that the Medium used in K&N air filters flows more than 300% more air than paper air filter medium when compared on a square inch per square inch [emphasis added] basis."

While this may be true, most if not all paper filters that the K&N drop-in panels replace have much more effective filter area that the K&N--4 to 8 times more due to deeper pleats and more pleats allowed by the physically thinner media. The substantially larger area of filter media in a paper filter is completely ignored in all K&N's assertions and claims about their media vs. paper.

300% more air flow per square inch through an effective area 5 times smaller equals 80% less air flow. This may account for some of the dynamometer tests showing reduced power with the K&N drop-in filters.

Manufacturers spend vast amounts of money playing the horsepower game, while meeting CAFE requirements. If spending $20 more per vehicle would improve horsepower and efficiency they would do it--they have no motivation not to.
2. K&N filters do not filter intake air as effectively as a quality paper filter, and I can find no claim made by K&N that they do.

They state that "...K&N air filters generally achieve overall filtration efficiency in the range of 97% - 98%...", and that "...[K&N filters] at times reach overall filtration efficiencies as high as 99% while maintaining high airflow...".  However, there is no claim that they filter better or as good as paper filters, other than perhaps an oblique comment in their FAQ that "...[we were] surprised to see some disposable paper air filters with an overall filtration efficiency as low as 93%." -- FUD (Fear Uncertainty Doubt) anyone?

K&N cannot legitimately claim that their filters are more efficient than paper filters (except perhaps the un-named "as low as 93%" filter) because they are not. All well conducted and documented tests I've seen have shown that paper filters are consistently more efficient when new, and throughout their service life. K&N also consistently qualifies any efficiency claims as "generally achieved overall filtration efficiency". "Generally" and "overall" - more fudge words...

The statement: "This process, known as depth loading, allows the K&N air filter to retain significantly more dirt per square inch than a paper filter." is interesting, particularly when speaking of drop-in panel replacements. As presented above, K&N drop-ins have much less effective area than the paper filters they replace. So, like the slightly better quantified "air flow per square inch" assertion above, this becomes a meaningless claim by ignoring the much larger effective area of paper filters.
3. Their FAQ is filled with more hyperbole, vague assertion, and false premise than "Dr. Bob's Medicine Show".

"We believe the primary function of an air filter is to deliver both high airflow and superior dirt protection" -- yeah, and I believe in motherhood and apple pie, there is nothing here stating that their filters do this...

"We design our air filters to provide superior filtration of the contaminants that can harm your engine while maximizing the airflow characteristics of the filter in question." -- an appropriately sized and gasketed piece of plywood would meet this criteria (it would filter out all contaminants, and have maximized airflow for "the filter in question").

"In fact, few air filter manufacturers publish any information as to the filtration efficiency of their filters." -- and other than their general design philosophy and the cherry-picked "...[results] ... for two individual air filters that each demonstrated among the highest overall filtration level we have achieved with our media specific examples of our best."  neither does K&N.

Much of their FAQ asserts that the K&N filter is superior to "foam" high performance filters (this undoubtedly true, those green "mushroom" things are horrid--my Lawn Boy has a better air filter). However this comparison is inserted into the text in such a way so as to imply that the valid claims made in that connection (K&N vs. green foam) are relevant to paper filters as well--this straw-man sort of argument occurs repeatedly throughout the FAQ.

From their FAQ: "Horsepower is a measure of the engine's maximum power while torque measures how quickly you can accelerate." -- If K&N seriously believes this then I seriously question the engineering expertise of their organisation.

In their graphic sidebar titled Disposable Paper Air Filters they state: "As fibers swell from moisture or oil blow-by vacuum pressure increases and airflow decreases." -- what is "vacuum pressure", I guess it's kinda' like "sweet and sour".

This section is also interesting in that it implies that "Turbulent filtered air." is bad, while in the description of how the K&N oiled gauze works its magic one of the is that "...turbulence caused by other particles and interaction with the air molecules cause these very small particles to become random and chaotic. As a result, these particles do not follow the air stream and their erratic motion causes them to collide with the filterís fibers."

K&N next claims that their filter's "Bonded cotton/wire mesh straightens air flow reducing turbulence" and delivers "Straightened and filtered high volume air" to the intake system (unlike those bad old paper filters).

Remarkable... I wonder what they can do for "dropsy"?

K&N's relevance to smaller displacement engines, most of which have air filters of huge CFM capacity as compared to the engine's needs, is marginal--they are aware of this which is why in nearly all of their literature you will see cubic inches used as a measure of engine displacement, and large block V-8's in the testimonials and sample calculations.

And finally, in February of 2003 I brought to their attention that they referred to the coarse grade test dust used in their testing as "course" grade (their reply and my message). They fixed this rather quickly in a couple of days, I have no idea how long it had been like that, however I think it amply demonstrates the actual level of technical expertise of the authors and readers of the FAQ.

I have found that it is pointless to attempt to alter the beliefs of "people of faith" using scientific evidence, and rational and logical arguments; all it does is galvanize them in their belief and label you a heretic and non-believer.

So, please don't bother to contact me, to tell me what a foolish twit I am or to relate your amazing experiences and 300HP increases attained just by dropping in a K&N filter--I won't bite and you'll be wasting YOUR time...

Some notable quotes from the K&N faithful (and my comments):

"I've got great faith in their filtering ability..." -- this one even used the word!

"I view all the "A to B" tests with some scepticism [sic]." -- especially those that don't prove what I know to be true;

" sounds great..." -- who cares if it's destroying the engine;

"I bought one because of the name..." -- they told me it was good so many times that I finally bought it;

"The car instantly felt a little more peppier on take off, idled smoother, and sounds good when taking off."
            -- any new filter would have accomplished "peppier" and "idled smoother";

"I like it, engine sounds good." -- gotta love that sound!;

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