One of the reps at work has a 99 grs and he told me bsides the greddy header he has, his aem tur pulleys gave him the biggest difference I did run with a few other cars this more and the second i would wind up and hit 5k I pulled out hard.....so i guess it did make a lil difference......I need a dc sports 4-1 header, but it will viod my warrenty lol