Just got off the phone with him, I didn't see your post quick enough Scotty, so I wasn't able to ask that question.
The pipe is a stepped head pipe, 1 5/8 out of the head to 1 3/4. They have a 2 1/4 full length heat shield back to the muffler, that is what gives the head pipe that big look. He said they tried a bunch of different sizes and this was the best set-up.
The muffler has a long louvered baffle in it. There is no packing on it, you can put packing on it and it doesn't change the sound very much.
They had a local customer loan them his C5 to do the R+D on it. He was having a hard time hitting 70mph on the freeway, now he is hitting 75mph no problem.