I'm planing on installing a S/C..... I currently just completed my cat back w/ a R.T. cat & Stillen Y-pipe, all of which are 2.5"! Now suddenly I feel the need for POWER! So I've decided to buy a S/C. What are the differences between having a 2.5" vs. 3.0", numbers please!

What is a S/C?

S/C = Supercharger...a company called Stillen makes a Supercharger kit for the '95+ Maximas.

To the original poster, I'd doubt you'd notice a big difference, atleast on stock boost.

I would go with the 3" if you plan on running 10 psi or more.

I guess what I'm trying to say is My 2.5 is pretty much new and was wondering what the performance differences are between the two? Are the gains significant enough to swap them out?

I would go with the 3" if you plan on running 10 psi or more.

3" is VERY VERY LOUD...
Just a warning...

PS: I dropped 4/10ths of a second switching from stock exhaust to 3" when i had my SC.

What company makes a complete 3" exhaust (not just the Y-Pipe)?

I think you have to have it custom made....

3" has 40% more flow capacity than 2.5"...