The 12579 is a large case single inlet, single outlet muffler. Internally the exhaust is split running the length of the case rejoining before exiting. The muffler has a nice quiet rumble at idle with no drone at speed. It has a nice performance sound when the throttle blades are opened wide. Install consists of headers, 2 1/4" to 3" Y-pipe, 3" through remainder.
I have a MBRP 4 inch system on my 2016 Ford F150 3.5 ecoboost, System gives great power but is loud as heck. When the original MBRP Muffler split at the seams I decided to give this a try. It's perfect. No raspy ricer whine or drone, It's deep and throaty, and not loud. Doesn't sound like a V8 obviously, but doesn't sound like Ricer Crap either.