The more air you can flow through the motor, the more power it will make. Note that is increased air flow through the motor, NOT pump more gas into it, NOT just make air flow into easier, NOR just make air flow out of it easier, etc, etc.....
You can't flow out more air than you flow into the motor, you can't flow more into or out of the engine ports than the engine ports themselves can flow, etc, etc. You can't flow more air out of the muffler than the pipes, Catalytic Converters and Exhaust Manifolds themselves can flow into the muffler.
You have to figure out the choke point in the flow in/out of the engine, i.e. the most restrictive and replace or improve that portion to flow more and match the rest of the "System".
I don't know where the choke point is on the 3.7L in the Commander, but I doubt the Muffler is it.
If I'm correct, just changing out the Muffler with a freer flowing version is NOT going to do anything to increase the overall flow of air through the system, thus NOT going to increase the power. In the past, like 30 years ago or longer, vehicles were much poorer designed, and often the Muffler was always the choke point, today vehicles are much better designed and the intake/exhaust is much better balanced and thus there are really NOT many choke points at all. Often on todays vehicles, benefits are only realized after a huge effort to replace the entire intake and exhaust system with a specifically designed package for you vehicle.
Perhaps if you've installed a bunch of intake mods, exhaust mods, etc, maybe even changed the cam and ported and polished the head ports and intake manifold, the OEM Muffler might become the choke point and only then swapping out the Muffler with a freer flowing version might create a real benefit.
Keep in mind, the OEM exhaust is Stainless Steel (SS). SS does rust, just much, much slower than regular steel. The heat and moisture of the exhaust will rust the OEM SS exhaust system, but often it will still last a decade past when that rust first appears. Meanwhile, a cheap aftermarket muffler that is made out of "Aluminized Steel" will likely rust out 2-3 years after installation, leaving you wishing you still had the OEM muffler on the vehicle. That's NOT to say there aren't plenty of good quality aftermarket SS mufflers that will last as long as, or close, to the OEM Muffler. Personally I would NOT pick an "Aluminized Steel" muffler to replace the OEM Muffler, get a SS version at the very least.
If you just want a throatier sounding exhaust, that's fine, just don't expect a simple muffler swap is going to do anything but that for performance. Also, don't expect the exhaust of a 3.7L to sound the same as a 4.7L or Hemi with the same muffler.
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Last edited by Mongo; 03-03-2016 at 01:16 PM.