The prowler headers wont fit into our engine compartment, cost about a thousand bucks, and only add 7-10 horsepower. The intrepids headers are not too bad actually, they dont provide much restriction. And too little restriction will cause your 02 sensors to mess up, and your check engine light will come on. A new exhaust will add about 10-15HP, one of the guys on the site claims to have 17 horsepower out of a Borla exhaust, although they are kinda pricey.