I need help with my 3000GT exhaust!! Ok first i need to know would the piping for a 1999 3000GT work for a 1992? and where can i find cheap parts for a 2.5" piping

 

A 99 exhaust should bolt right up. I believe their is a 1/2" diameter difference between the NA and TT exhaust. You won't get any performance gains from the 99 exhaust as they are the same.

Cheap 2 1/2" piping, check your local exhaust shop or maybe a chain like Midas.