These guys took all the common air filters and did a bad ass test with 'em. Check it out:

http://home.usadatanet.net/~jbplock/ISO5011/SPICER.htm

 

interesting.

 

k&n lol

 

Cliff's notes!

 

You're a lazy son-of-a-bitch. There's your cliffnotes. It's a study, how am I supposed to cliff a scientific study?

 

Like so:
Cliff's Notes
K&N FTL

 

AC Delco 4TW?

 

Now you're getting the hang of it!

 

hahahaha K&N might give you 10hp but it will kill your car three times as fast as a stock ACDelco filter. Slow is better.

 

Bupkis. Sucking in a little dirt isn't going to kill a car. If you've got a K&N filter on your car, you either actually have a performance vehicle that needs more airflow, or you think you have a performance vehicle that needs more airflow. Either way, beating the shit out of the car on a daily basis is more critical than letting a few microns of dirt slip by the filter.