cheers for the replys only reason I want to do the cat back and growler is warranty reasons other wise I was thinking cooler, injectors, air, 4in dump in to 3'5in or twin 2'5 and 14psi tune I guess I got to make my mind up about if I risk it. the r8 I did full exhaust, air, cam, tune 22in rims sitting on its cuts have a look at pic