We've all seen the dyno pulls showing a drop in hp from swapping oem filters for aftermarket, but what is this really from obviously most will think its from flowing too much air and creating turbulence in the air box but has anyone ever checked? actually flowed the filters to see if this is the problem? One thing to consider is maybe they are flowing less air from being able to filter out smaller particles. If this was found to be true i would much rather be down a couple of hp and keep my motor as clean as i can on the street. and keep a set of oems for the track if i found it that necessary.