I can't seem to find it anywhere, so don't get mad at me. Yes I know how to search. What is the official diameter of the GMP exhaust cat-back? I am considering altering my set-up in the near future if it really is only 2.25" cause I just got stage 2.

 

2.25" is correct.

my car made no more hp on the dyno with an open downpipe than when flowing through this exhaust. so you know it flows really well!

 

2.5 is not correct!!! it is 2.5 all the back except for about 12" right before the muffler which is 2.25

 

hes not talking about the stock catback, he's talking about the gm performance catback...which is 2.25"