what is the stock diameter of exhaustpipe around the muffler on a 3.8 99? The pipe around the cat looks alot bigger than the rest. What size is that where the two pipes from the manifold meet? and what about after the cat? Thanks.

 

After the cat is 2.25id

 

is before the cat 2.25/2.5 too?

 

before the cat is 3" and the rest is all 2.25"

 

This shows you all you need to know (2001 Camaro RS V6):