How is a cat back exhaust, regardless of configeration, 3.5 single or 2.5 twin etc etc, going to add 40kw? I thought that other peformance add ons like intercooler, dump pipe, cat, tune and turbo psi that make the most gains kw wise. Of course everyhing works together. There are cars on here runing relatively high rwkw's with standard cat back exhausts. I thought I could do the same and that an exhaust, kw wise, would add modest gains to the existing rwkw. Anyone know what kw gains a cat back exhaust on it's own will actually add? Thoughts? Oops, the $895 quotes for injectors actually was for purchase and fitting only. Tune was extra.