So- all you guys are going to pounce on me but here is my actual results
2.5 97 TJ
Installed 2 1/2 in high flow pipes and turbo muffler, plus magnaflo cat.
well it was noisy, dronie, and sluggish off the line.
So i cut off my new stuff and installed a factory size system with muffler. left the cat.. well... WOW 2.5 need back pressure!!!!!!!! end of story
Big pipes are good for V8s but not for 4 bangers.
now is quiet er not that quite though.
and so peppy off the line.. really happy