when I had a 2001 GT a great combo was u/d pullies and timing adjuster from Steeda. good bang for the buck. I was wondering if advancing the timing (with a diablo tuner) and a set of pullies will have the same effect? (on a 2005 GT) Is the Magnaflow axle back exhaust a good purchase? will it help add power? Or is borla better? I was looking at the magnaflow kits and noticed that there is a 2 piece and a 4 piece, what is the difference?