The K & N and other aftermarket air filters

12B
k _n.htm

 

This is edited from an exchange on the Airheads LIST:

((note:  earlier portions of this exchange were on the K & N, Uni, etc...))

 ... although the Uni Filter sounded good until they stated that I may have to rejet since their filter provides greater air flow than the stock... Any Hedz have experience with the Uni Filter and rejetting?

Someone replied as to a posting of mine:

Note where 'bum stated: "BMW filters have a vastly larger filtering area than required?"   This means the BMW filter is not strangling your engine.  This means your engine will demand no more air with a supposedly better flowing filter than it does with the BMW filter and this means you don't have to rejet.  This is all mythology ... as are the majority of aftermarket component claims.  If the BMW filter provides "more than required," what difference does it make to provide even more than that?  If, in the highly unlikely event that's a true claim.  Unless you do one or more of the following ... increase engine displacement; increase intake valve size; increase cam lift/duration; find a new redline......(then) your engine will continue to ingest the same amount of air and your carbs will continue to mix in the same (correct) amount of fuel.   Without changing these things the only way to get it to take more is supercharging or turbocharging.  That is, you have to force it in.  Filters are neither.  (even those called "filterchargers.")  The aftermarket are the real "stealers."

To which I replied:
No disagreement in the slightest.  xxx   is basically correct on all counts.  I suggest you Headz read ALL of what I have, below, rather than pressing delete immediately...as I DID TESTING. I might add that the changes to engine and rpm would have to be VERY big changes for the stock BMW filter to be inadequate.    I got into all this once upon a time on this LIST, long ago, but, ...here it is, again...sort of anyway:
My supercharged /5 went for normal mileages between STOCK filter changes; around 20K for me;....and, I did measurements on it in the same way I did much later to my first R100RT:      I used an old super-sensitive aircraft gauge that is a dual type (separate elements, twin needles).  I also have a differential altitude instrument that is even more sensitive, and reads out in inches of mercury.  ANY of you with ANY type of manometer, gauges, whatever, can pretty much duplicate what I have done.  With one side of my dual gauges connected to the intake side of the filter, the other side connected to the outlet, one can crudely measure the difference across the filter.  If the 'piping' is properly positioned to avoid venturi and coanda, etc., type of effects, this really works rather well.    I have tested the stock filter on my R100RT when brand-new and when it had over 20,000 miles. I put a REALLY filthy old customer's filter in that bike and re-tested.   Maybe three years ago, on the SAME R100RT, I also tested a brand-new K & N filter that I specifically purchased for measurements (then I sold it off my website).  I tested the K & N before oiling, and after oiling it with K & N filtercharger red fluid.  I had an old customer's K & N filter on the shelf, that was quite filthy, and tested it.  I also tested it with a dirt bike foam surround added.   I also tested a BMW 2002 car filter (round type), that mounted on an aluminum plate, sealed to the top of the lower part of the rectangular R100RT airbox.  Also on the same R100RT.   That filter was noisy, susceptible to water damage (I never made a hat for it), but the results of ALL my testing was pretty clear.    Bottom line:   I use the BMW stock filter myself, with measurements to back me up.   Up until maybe 4 or so months ago, I had on my website for a longish time a couple of hyperlinks to two different websites that had the information from independent laboratories that measured the actual particulate filtering capabilities of many filters, including the K & N, which were tested extensively and the reason for the hyperlinks.   The K & N was not favorably regarded, to say the least.   The hyperlinks kept getting messed up as the website owners played with the websites, and I got very tired of having to find the articles on the websites, as folks told me the hyperlinks were not working.  I removed the hyperlinks, don't even have them anymore....but a Google search would find them.

 

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