Here are the parts for one muffler. My friend with the BME designed them and had some of the machining done and I welded them all up. I think we made 8 all together so we all had some to play with. Its a similar layout to some of the commercially available cannisters.
The small tubing is .875 od .049 wall for the inlet and outlet. The larger pieces are 3" od .049 wall.
Ive made a couple of variations on this design that were a little less complicated and were still under 90db on the 46cc Poulan and didnt loose as many rpm.
Adam