I'm using a RAASK with about 1 foot cut off and the baffle in the HD-FXD muffler would be about the end of the original RAASK. When I tried a HH Drag Pipe for a couple days, I lost about 8 mph on where I could run in 5th gear. 43 up from 35. High end was probably better. With the set up I have I'm back to 35-37 in 5th as minimum where it will pull cleanly to cruising. I'm hoping this company will develop a suitable high torque/ high HP muffler,
http://www.performance-design.net/index2.htm. They have designed one that provides both torque and HP results. Years ago I had a book with a formula in it for max torque length of intake and exhaust tract or conversely max HP at RPM. In the early 70's I had a Honda SL-125 I modified and used for observed trials and commuting. I had lightened it to 200 lbs, had high back pegs, CT90 seat cut down, Preston Petty fenders (rear with light), removable headlight, and a Powroll stroker kit with a hand made exhaust from bits and pieces with a round flat muffler, forerunner to Supertrap I think, exdusher?? Had amazing torque for 150cc about 1600 - 2500 RPM. Did well in amatuer trials of the time with it. I have looked in vain for the book and/or formula since. It must have been loaned and not returned or lost in moves over the years.