I will never use K&N's again. I did have a pair in my Crossfire at one point, but after reading up a bit on them, I would recommend to anyone to stay away.

What it boils down to is that they flow a little bit more because they do not filter nearly as much dirt.

Is the tiny hp increase worth the extra dirt that is getting into your engine?

http://home.stny.rr.com/jbplock/ISO5011/SPICER.htm


This is also an interesting test, although not nearly as scientific:

http://www.bobistheoilguy.com/airfilter/airtest3.htm