an engine is no more than a fancy air pump, the more air you can make it suck in, and the more exhaust you can blow out. the more power you make. there is testing that proves k&n filters filter more air due to a larger media in the filter. i think they filter down to like 2 microns or something. yes you wont get a miracle in a box, and a filter wont give you significant boost, but the fact of the matter is, it will give you a little better throttle response, a little better gas mileage, and a little more hp. but its not drastic. i know some of you will say that your factory intake is already a "cold air intake" and i to some extent agree, it is getting cold air as apposed to having a filter in the engine compartment. but from personal experiance, and also coming from the turbo world, if you can make your own intake piping, route it so it gets fresh air, put a cone style filter on it, and make it so it has a smoother path than the factory, then you will notice a decent improvment. now, i know some/a lot will flame me for this by saying that the factory system is the same size for the 2.9, 3.0, 4.0, ect. this means nothing to me, just because they use the same size on all these cars doesnt mean they dont have restrictions, and yes an intake is not the most restrictive part of your car, i will agree 100%, the most improvement is opening up your exhaust, bigger throttle body, head work, yada yada. but thats my $0.02