Having had tons of hands on experience and "sit down" chats with engineers. 2.5" piping is recommended on a car like the Z32. One 3" pipe can flow 900 HP, imagine that? We have dual piping and you want 3" piping? We hope you can make 1800 HP! 3" piping is way too big and slows the exit speed of the exhaust. Not to mention it can create unwanted turbulence; loss of low end response & power too.