the only concern i have with the gundo hack is that i can see that the gasses exiting the mufler will have to fight with the bypassed gas also heading for the exit.

the 2 exiting pipes are not positioned in a way that will make them flow into each other the way you see a merge collector bring the header pipes together in a harmonious flow.

the angle at which the bypassed exhaust joins with the muffler exit is at odds with each other and there is probably considerable interference with the 2 flows trying to merge into 1.

would like to see a dyno for this if someone gets around to it.

the 1 benefit i can see is some of the exhaust does skip the muffler but i dont know if thats enough to overcome the merge angle