2 1/2" vs 2 1/4"

doing a catback system and now due to someone's comment im wondering if a 2 1/2" pipe will really be better than a 2 1/4". this would be going from a 2 1/4" out of the cat to 2 1/2" out back. any real benift to this, or would this actually hurt things. ie loose too much backpressure or velocity?

Going to 2.5 out fromm the muffler probably will not hurt but I do not see how it will help either. My XJ came with 2.5 from the down pipe to the muffler then 2.25 from the muffler to the tail pipe. I replaced the cat back with 2.5 all the way to the tail pipe. Later I reduced the tailpipe to 2.25 in order to reduce the resonance. Performanance remains exactly the same with both the 2.5 and the 2.25 pipe fron the muffler back.

Bear in mind the 242 cubic inchs of the 4.0L do not produce enough exhaust velocity to maintain proper flow/scavenging when the gases cool through that long exhaust system all the way out back. That caused high resonance that I disliked particulary at cruising speed. Most people on this forum enjoy hearing the sound from the 2.5 tail pipe.

guess i need to go remeasure. i coulda swore it was 2 1/4, maybe thats the cat outlet? the down pipe does look meaty. well i hate resonance, so im all for that aspect. i need to measure to make sure i get the right muffler. what muffler are you running?

i guess in answer to my own question i just saw in your post below to my other post that you are running flowmaster

so went out and did some measurements and the downpipe to the cat is 2 1/2" but the output on the cat is 2 1/4"