SwifTT

drop in filter. From my own experience so far, if you're planning on a K&N or any other air filter, and would like to actually FEEL an improvement, I would suggest you tune(ie chip) your car first. If your car is stock, with a K&N is basically useless because it does allow more air flow, but your ECU doesn't seem to 'need' the extra air and by that it wouldn't take advantage of the extra air. Personally I installed my filter along with my Forge valve, and thats after my chip and exhaust, and I noticed improvement right away after a short drive. I can HEAR its sucking in more air and the throttle response did feel a little more crisp. The air filter is kind of like a part of a package, you can't have it working by itself, it would (some may argue..) be useless. But then again, I don't have anything to back my theory up, but its just from my own experiences, so I may be wrong and just comforting myself about the $50 bucks I paid to get the K&N..but luckily this isn't the case for me

gtt

you always want to balance intake and exhaust and engine in between. The entire system is engineered for performance, exhaust and driveability. Many times going away from stock with just an air filter or just a pipe does nothing if not worsen performance. K&N's can make more noise as the filter and mesh screen can resonate and if you remove the housing of course it will be louder. Dyno is one way to test power, otherwise you may only be fooling yourself and unloading your wallet to some aftermarket company that has a very good marketing/hype department. Don't assume anything and shop from proven companies that have proven performance gains that are documented not merely hyped.