Not too hard to have a test unit made-up......or add to the 2-inch if you know the 2.5 was an improvement. I do exhaust tuning on my single-cylinder landspeed bike to run at Bonneville.........On the first attempt we were lucky, no carb changes were required for the change in altitude, just removed the baffle completely to run best at WOT.
My brother-in-law built his CB750 to an 836 with a mild cam and Kerker exhaust. Too bad he stayed with stock carbs......the bike actually runs much better on the highway with stock 341 exhaust pipes.
