i'm thinking about getting a CAI for my ej but will i even feel a difference in performance with a stock motor and if so whats the best system out there, thanks...

 

Yes, your lower end power which already suffers will be less, but your feel faster on the upper end on the butt dyno.

Most cost effective mod i've tried for d-series motors is a good header. If you have a vertical tb manifold, swap it for a horizontal manifold.

An intake and a catback will be noticeable, but you wont be much faster if you are at all.