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.
Had what I was told was a broken manifold so I got these and combined them with high flow cat converter and duel exhaust from magnaflow. Installed one side which was very hard due to lack of space and bolt pattern behind some pipes. Found out I had a broken bolt on other side and had to take to specialist who said this was a common problem with my motor. He finished the installation of the system. Noticed increased torqued and power and engine seams to run smoother. I'm happy