i just removed my cat and y pipe because ill be getting my headers and y pipe on monday or tuesday and i gutted my cat and got all that crap out of there but i need to know what size pipe i need to run inside of it? i want to retain the cat look so i am running the pipe through it. i tried measuring it but one end is smaller and the other end is balled out and it looks like i gets smaller as it goes into the cat. anybody done this? if so what size pipe did you use? im goin to autozone on monday. if it matters my cat is from an 85 trans am and it had an lg4 before the motor swap.

 

just put a straight piece of pipe in its place, and take the heat shields off the cat, and weld them around the pipe....looks like a cat