I think the stock over the axle pipes flow just fine. I'm sure a good cat back system like Magnaflow for example with some Magnapack mufflers might get you 3-5HP on a good day, from the research I've done, if you really want to pick up some serious HP from an exhaust upgrade you would need to do LT's and a hi flow H or X pipe (American Racing makes nice LT's and a hi flow catted H or X pipe) When I say serious HP I mean somewhere around 25-35HP, does not sound like much, but pretty substantial over the stock system, and I think the price tag for a system like that is somewhere around 1,295-1,600 depending on the finish of the headers etc.....
But to answer your question, I believe a cat back system is only worth 3-5HP so IMO that makes this $500+ mod really just for sound. I have no proof that you gain only 3-5HP with a good cat back system, this is only the knowledge I have from doing research.
I'm sure someone else will chime in here and give you more info.
I should also state that if you did LT's and a hi flow catted H or X pipe, you would also need a tune, so depending on the tune you get you could get somewhere around 40-60HP total, and you would have to spend an additional 379.99 for the tuner, unless you were to get a Dyno tune, which I dont know the exact price for a dyno tune.
Yeah, pretty much only good sound. You need to work at the front end of the car if you want to make power. L/Ts, X, intake, manifold, computer tune, etc is where the power is.
I could feel a little bump in power after the Borla ATAK catbacks (with x-pipe). Like everyone else said, it's probably minimal but the exhaust sounds amazing and it's worth it for me.
I could feel a little bump in power after the Borla ATAK catbacks (with x-pipe). Like everyone else said, it's probably minimal but the exhaust sounds amazing and it's worth it for me.