I recently installed the \'made exclusively for 4wd\' Magnaflow performance exhaust system on my \'11 JK unlmited Sahara. It claims a dyno rated 10hp and 12 tourque increase, for what that\'s worth.
Looks - The polished stainless exhuast tip is nice (and the same with the muffler). You can\'t really see it much so that part doesn\'t matter much.
Sound - modest increase that is fairly quiet when you idle.
Install - The hardest part was the removal of the old setup - I haven\'t done any exhaust work since I was 20 so it\'s been a decade and not much experience to boot - that being said this was pretty easy, just required some patience. Start to finished cleanup was 3 hours.
The ground clearence was enough that I didn\'t have to jack up the jeep, a bonus (and safety wise much nicer). I highly recommend at least a decent electric heat gun to help separate the old pipes and muffler and to help remove the old exhaust from the rubber hangers. I did have to remove the tranny skid plate to get the old exhaust pipe off and around the axle.
The new mandrel bent exhuast is very nice and easy to install, uses the factory hangers and comes with new pipe clamps. Make sure you check for clearence before doing the final tightening of the clamps (I started with the rear last clamp at the muffler and worked my way proximal to the cat--the muffler and over axle portions were the only place that really needed adjusted for body clearence.
After install, I have noticed a modest exhaust note increase and an appearent improvement in throttle response. Nothing amazing but it is present. This, coupled with the K and N cone intake, has given the impression that the engine isn\'t working as hard for the same performance as before, and it has a bit (just a small amount) more power it appears (maybe I am trying to make it seem that way). At $366 for an all stainless magnaflow setup (for this version, which is identical to the non \'made for 4wd.com\' version), it\'s hard to pass up if you are looking at a modest exhaust change for a daily/occasional offroader.
