Bro, I agree with cdpascual initial performance gainer would be Intake/Header/Exhaust modifications. If you modifed the Intake plate filter (K&N) then you have to modify your header (use S/S Mandrel bend headers) and an aftermarket exhaust chambered/free-flow muffler ( ex.Tanabe G-Medallion) plus a layer of thermal wrap to ever notice performance. If you can afford a Cold Air Intake that would be better, with all this modifications this would surely void your warranty.

Cheers,