I have a stock muffler on my Z right now. I want some additional horsepower but I don't want a muffler that is really loud. What brand & model number is going to give me the best performance without the really loud sound?

 

You aren't going to gain much, if anything by just replacing the muffler. You still have 10 other feet of pipe for the exaust to travel through. That last foot isn't going to change much.

http://zbum.nissanpower.com

 

What would you recommend for replacing piping on my exhaust system? I'm not sure what size the stock tubing is but I''ve heard sizes from 2 1/4 to 3 inch tubing is recommended. To replace the stock tubing with larger tubing does that require a new catalytic converter?

 

with an NA, unless you are heavily modded, a good 2-1/2" cat back system will give you a little. Add headers and pipe before the cat and you are golden.

with a turbo, the turbo provides all the back pressure you'll need. Go with a full 3" and turn up the boost a little.

http://zbum.nissanpower.com