BryanTT

Sorry to bring up a well covered subject here
in the forum, but my research into K&N filters
(thanks for the assist RoberTTo)left me more
perplexed. I know the differences between stock
and aftermarket filters are minimal at best....
but are K&N drop in filters actually detrimential?
Help

Jim TT

A K& N filter uses four layers of cotton gauze between an epoxy coated aluminum screen. They start a filter design by reverse engineering a stock filter and commit a CAD design layout. This layout is executed on a CNC machine on which a mold is cut. K&N does extensive flow testing of OEM filter elements with the goal of achieving an increase in flow of 10% to 20 % thus preventing the need for re-jetting in non fuel injected engines. Because of the efficiency of the K&N design they can produce a filter that while the same size as stock, flows better. Car manufacturers consider the cost of air filters very carefully and a filter like the K&N is simply too expensive to do as an original equipment item. I have used these filters for 25 plus years on motorcycles with good results. However as air box designs have gotten better and better there are less power robing restrictions in them, so gains are tuff to get. Still K&N gives you a filter that you can clean and reuse, so it can be that last filter you ever buy. I have discussed the TT application with several tuners and the consensus seems to be that you will see a slight improvement in throttle response but not much else. FYI the first layer of dirt on a K&N acts as an initial filter medium. But over time the element gets real dirty and the special K&N oil can evaporate. So it's time to clean and reinstall following their instructions, what ever you do Don't use compressed air to clean one as you will ruin it. JIM

BryanTT

Wow...Thanks Jim

Bluto

Great info, you have one on the TT?

TTop Gun

...and some have reported finding excess dirt in their engine oil that they attribute to the K&N filter. Oh, but they use them on all of those off-road vehicles, you say? Keep in mind that they are mostly competition vehicles, and see *daily* fluid changes for the most part.

Also, in a VW application that I'm familiar with, I believe that I discovered the factory paper air filter having somewhere in the neighborhood of 10 times the surface area of filtering material than the same K&N filter for that application. Do you think that K&N's filter passes air 10 times easier than the paper? Not me.

One closing thought. Is the 0.005 horsepower that you might gain from a K&N filter worth the possible damage caused by sucking grit into your hamster-charger??? No, thanks, I'll stick with the factory filters.....

Jim TT

...oil in has to get past the rings, because it is not traveling up the valve guides and past the valve seals. I think the dirty oil is most likely from an other source but would need to know a lot more. JIM

Jim TT

No I use the OEM filter which I have changed once.

Auto Union Jack

Two, the filtration rate of the K&N is 5 microns. There is a lot of dust out there smaller than that. The BMC is the same design and filters at 2 microns (smaller than dirt). This filter is used extensively if F1 by factory teams and comes from the factory on Ferraris and Porsche Cup cars. <ul><li><a href="http://www.bmcairfilters.com/">BMC</a></li></ul>