Originally Posted by Cattman

As with most mufflers, there's no relevant power gain or loss.

Here's how an exhaust typically works: gasses pass from the engine through the headers, into and out of the cats, then into the mufflers, through the muffler baffles, then out the muffler and into the air. Mufflers have an inlet pipe and an outlet pipe, and in between is the muffler "can" which may contain baffles. With the Gundo Hack, you are adding a connection pipe between the muffler inlet pipe and outlet pipe such that some of the gasses coming from the cats bypass the muffler's baffles altogether.

Hacking your OEM mufflers in this manner is similar in sound and basic principle as the PSE, with the primary difference being that it's not switchable on/off.

I am currently running AfterHours mufflers with AWE cats, and will swap to Gundo mufflers with AWE cats this weekend, and post some clips, meanwhile, here is a photo of a set of Gundo hacked mufflers that shows the small 2" diameter pipe connecting the muffler's inlet pipe to it's outlet pipe, which allows some undefined percentage of the exhaust gasses to bypass the muffler baffles/ can:


And here is a clip of some similarly hacked mufflers with stock cats:

http://www.youtube.com/watch?v=Vf0NpWNAj78

CATTMAN