I bought a used LT1 magnaflow and had to cut the I pipe down to fit my Y. The magnaflow is 3 inch OD. Without getting back under and taking it apart I need to know the size the tsp ory pipe that will be bolting to the cat back. I swear is was 2.5 but not sure if it's od or id. I'm going to buy a reducer and weld it to the I pipe then clamp it to the y. It's just way too lose fitting right now to seal. I emailed tsp and they said it was 3inch but it is not. Just wondering if anyone on here knows off hand so I don't need to take it all apart.

 

It is a 2.75 ID which allows it to mate up to the stock catback and many other catbacks

 

I just got a used Magnaflow catback, and the I-pipe had a little bit of a step-down which was the perfect size for my TSP off-road Y...

 

The connection size is about 2.75". Just about every catback necks down to that size so everyone's exhaust will bolt up to eachother.

Jon