We I got my 91 xj , 4.0 4x4 ... I got a fresh motor and trans and I'm at the point were I need to get a exhaust set up to smog it. As of right now I got a O.E. cat and a Magnaflow muffler clamped right to the cat and then dumps out right outta the muffler.... wanting to know if there will be a difference if I buy the rear tube to go over the axle or if having it dumped pre axle will be the same... I want torqe of coarse so if adding tubing will give me torqe then I'm down to do it..... any thoughts

 

Run it to the end of the bumper the way they did it stock. Torque wont be effected, it will sound a lot better since the flowmaster gets real loud about 3K rpm's, and If the emissions stations do not have easy access to the exhaust they will not run the jeep through till you lengthen it.

I would recomend a header for noticable power gains. A shorty would work fine for a street vehicle. I install them on every vehicle I own.
http://www.sandersonheaders.com/Lets-Get-Technical.html