ORIGINAL: The_Pipefather
If that is the case then I bet using a stub exhaust will definitely be an improvement over both open exhaust & silencer?
That s how we tested our engines. A stub of tubing the same dia as the original header and about 6 to 8" long (on a 125cc engine) would remove the undesired reversion of exhaust gas during the upstroke (& the resultant messing up of jetting/carburetion), and also improve exhaust velocity over open condition. This was the baseline condition for checking changes in intake duration, intake length and carb dimensions.
Anyone willing to try it out?
You are correct -- I quite agree -- except that either an open exhaust, or a stub pipe are unacceptably loud in most jurisdictions. Hence, muffled tuned pipes, resonant mufflers & unbaffled stock mufflers.