[Zeke]

As someone pointed out recently, once you cut the holes for the dual outlet pipes sport style, it's a direct shot from the inlet. I see no reason anymore to do any intenal cutting. Maybe that makes it a bit quieter, but it doesn't open it up any more unless I, too, am missing something in that drawing.

Same for the right end pipe mod. That opens the chamber up to the outside and, like Wil says, the gasses are now allowed to exit directly thru the right pipe. Whereas, they still have to go thru the system to get out of the original left pipe.

I think the internal holes cut as shown would be more appropriate for a dual out, side exit unit. BTW, this only applies to dual in mufflers. I have no idea what the flow pattern of the single in muffler looks like. And JBO didn't tell us what he has.