[f5fstop]

It is a lurking smiley. Just hanging around to see the answers.
I know for a fact, that on my Vette, a straight replacement K&N filter did not do a darn thing to increase HP at the dyno. (Tunnel ram systems such as Veraram that use these types of filters do show an increase in HP on a dyne; however, these are completely different types of air intake systems, not just a straight filter replacement.) I also know from reading reliable reports online, and seeing the test results one manufacturer did on approved accessories for vehicles, that any cotton oil coated filter allows in more particles than a good paper element.
As for fuel mileage, I have never read anything in regard to this, other than K&N's own biased information, but cannot believe the mileage would increase and if it did, only by a minimal amount.