ITRCA

So I've found what I need to fix my exhaust. My friend gave me one piece of the few he has, but the ID is too large. What is the ID on the exit side of the cat? I think he has 2.25, 2.5 and 3.0 pieces. I know its obviously not 3.0 and I'm 99% sure its not 2.5, but I wanted to say it was 2.36", not 2.25".

What I've got is a "header extension", so we can just cut the pipe to fit and weld it onto my b-pipe.

It sounds like you are extending your 'B' with that weld.

My 2000 LS had an OEM 'B' pipe and its inside diameter, which attaches to the cat, is 1 7/8"

The part number, for my LS catalytic converter is the same number as the 2000 GS-R.
I never checked the part numbers of the 'B' pipes, for these 2 cars.