iv got a standard uk bugeye wrx, just got a hayward and scott up pipe fitted, and i want a vortex afterburner exhaust,... so do i just need the back exhaust for that? or will i need the whole exhaust system? my wants are the sound, and the extra power, i guess i already have a cat in the down pipe and prob another somewhere in the exhaust, do i need to de-cat or will buying the afterburner do the job?