After careful consideration, and speaking with Jim Bisson, I decided to cut the rolled ends off. In fact, I completed the task last night.

I was told that the exhaust end open area should be around 60% of the exhaust port open area (which is .6 sq in). With the rolled ends I was at 42% (.25 sq in) running 6600 RPM. The down draft muffler was at 72% (.43 sq in) running 7000 RPM. Now that the rolled ends have been cut off of the Bisson, the open area at the exhaust end is 80% (.48 sq in).

I will run the engine this weekend to see what gains I will make in RPM. I will be sure to post it for all of you. This may be a valuable experiment for you who have rolled ends on your mufflers.

Ryan