I use jpc overaxles. they are an important piece in the power puzzle. To get the most out of them you need the best flowing muffler. I use roush. My car is louder than A GT350 with borla atak system I've heard both on a dyno.
You can get them from lethal performance or from LTH if you want the satin finish. These pipes are all manufactured by a company called cp-e. I use them to complete my exhaust setup with kooks headers offroad x pipe and corsa sport quad tips