Well a couple reasons...I looked up the possible oil in the MAF issues, dirt build up etc etc but I'm not too worried about it. I wanted the .0005 more MPG since I use my X to commute 80+ miles day! I've had k&n's in all my NA cars for more than 15 yrs w/o any issues. Afe drop-in my E36 for the last 4 yrs.

No seriously...my filters needed replacing and after inspecting the air box there was quite a bit of sand/dirt in there. They're still building houses on my street/neighborhood and there's plenty of sand flying around so I thought I'd give this a shot and see it if helps any...will be checking it periodically. If needed I'll go back to stock.