exhaust- dual versus single 2 1/4 versus 3\" After the headers it's time for exha /forums/images/graemlins/pimp1.gifust. I need an education. I see single cat-back and turbo flow exhaust systems that are 3". (What is a cat-back anyway?)and I see duals that are 2 1/4. What are the relative advantages and disadvantages of each? Why not dual 3" pipes?