I was looking at my exhaust pipe today and I couldn't figure out what the stock size diameter it is. Anyone know? Looks like it gets smaller on the bends. It's going to be replaced with a 3in Flowmaster with high-flow cat but I am still curious.

 

I got an 87 transam gta, mine was 2.5 when I took it off and measured. I have the flowmaster catback, its pretty good, I'm take off your heat shields and dent them back before you put on your exhaust though. I've had to work on em 2 t imes so far, it would be easier to do it while the exhaust is off.