Originally posted by: WISTECH
One of the guys I ride with bought a 400ex new last year and installed a k&n right away. He is already complaining of oil usage and and a small amount of smoke. Next time we go I will do a compression test and check the intake tract. We have been riding severly dusty trails all summer .I mean trails so dusty you have to space each other out half a mile till the dust cloud settles so you can see. I used to use them a lot but I had several engines with prematurew wear. I have noticed on my factory foam filter it will look like hell on the out side but on the inside it is as clean and white as new. Again you guys should check out some of these web sites that are testing these things for air flow and filtering efficiancy. I still believe they would be ok for winter use or maybe in sand duning because the sand is large grain . But fine dust is another matter. Its your engine so a little research could be worth it.

Originally posted by: vampireforeman
just stating what my local dealer said to me.....they said their tech's could tell if i had been running a k&n...i don't see how either......is there a noticable difference when you add a k&n?