Stock catback is good up to liek 350-400hp.
Do not get a cold air intake get this instead AEM 9"X4" CONICAL DRYFLOW AIR FILTER ELEMENT 21-2059DK | eBay and search for Nawarkk's simple intake thread.

Oh and read this thread many many times, I wish I would have know about it before I started buying **** for my car. http://www.grandprixforums.net/safel...car-17482.html