Even though I posted this on another thread I will post it again on a dedicated thread.
I just installed a Magnaflow muffler (part# 12589). I noticed a couple of things while being under my truck and actually looking at the exhaust. On a 2007 H2 the exhaust pipe from the catalytic converter back to the muffler is 3 1/2 inches. Just like all aftermarket cat back systems. It does reduce to 3 inch's about an inch or so before the muffler, then after the muffler it goes from 3 inches back to 3 1/2. The pipes are mandrel bent from the factory and are positioned about as good as you're going to make it. So why do we need to buy full cat back systems? Is it because of the stainless and it looks good before you decide to go mudding? Is it the quality of Muffler? Magnaflow has been making Mufflers longer than most, so I think they have muffler tech down by now. Is it the mandrel bends of the pipe? The factory uses mandrel piping as well. Could it be the irritating drone at speed of the muffler?? Nope, I have absolutely no drone.

So I think cat backs are a bit hyped, but hey, who am I to tell anyone not to spend 1200.00 on a Corsa Cat back?

By the way, the Magnaflow sounds like stock at idle untill you rev the engine up then it sounds very throaty. Driving around town sounds great and getting up to speed on the highway...priceless.