Here is thread I started.

https://www.cherokeeforum.com/f59/muffler-comparision-sound-horse-power-139223/

Here is sound comparision on mufflers on Cherokee
http://www.youtube.com/watch?feature=endscreen&v=SFq-fToDlXA&NR=1

Here is decimal sound and horse power comparision on mufflers
http://www.mustang50magazine.com/techarticles/m5lp_0212_ford_mustang_muffler_comparison_test/viewall.html

 

i ran true duals under an '84 cherokee that me and my father rebuilt, though that jeep got a 4.3L chevrolet v6 with 3.8L heads, flo-tek motor swap headers, a turbo350 trans and a t-case out of a '93 grand cherokee, i used a pair of 18 inch long cherry bomb glass packs, and she'd run down the highway without problem, and had no problem on the trail, but there again i was taking two banks of cylinders and evacuating the exhaust gasses, the cherrybomb Si/Do mufflers do sound good, but for a stock inline, its more of a matter of taste vs performance gain, but thats just my .02 cents, not a bad setup though happy wheelin'