right now i have a stock exhaust up until my flowmaster muffler, which splits into 2.5" duals. My stock pipe size is 2 1/4" i think, and im gettin a new high flow cat to replace the 2 that i have on there now. what i was wondering is would it be good to go with a 3" pipe from the new cat all the way back to my muffler, since its a 3" opening and the exhaust shop only put 2 1/4" piping? its a 96 f150 302

 

It sounds like I have the same muffler you have, 3" inlet/ 2.5" dual outlet. It's not a problem if you have a cat with a 3" outlet to connect the inlet of the muffler. I'm running 2 high flow cats (dual 2" inlet/ single 2.5" outlet cat into a single 2.5" inlet/ outlet cat with a reducer from 3" to 2.5") After the muffler I ran all 3" pipe exiting the driver's side and passenger's side on a 45 degree angle but you can run 2.5" pipe. Hope this helps.

Warr