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Deleted member 12676
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I believe the 11mm inner diameter of the stinger of the standard muffler is correct for the 69cc, not the 48cc. Dividing 48 by 69, and multiplying it by the cross sectional area of 11mm gives you the area that a 9mm stinger would give. I reduced mine to 8mm to try it out and there was no change in how it ran but the exhaust note was reduced in sound level. So if you have ugly neighbors giving you the evil eye every time you ride by you may want to try this out. 9mm can be had with a 11/32" or 3/8" drill bit drilling into semi-dry JBWeld that was filled in for the last inch of the stinger.
I regret that people spend good money on expansion chambers that are designed to create a very loud exhaust note. They do that by having the stinger begin at the end of the last cone where the exhaust pulse has been concentrated down to the smallest size so that it has a higher pressure. That high pressure exiting the stinger (or the silencer) creates more noise because of the greater pressure difference between the exiting pulse and the outside air. That is my first gripe. Second is that they reduce mid range power in order to increase top rpm power by means of a steep angled baffle cone, which is a design only beneficial to racer engines with transmissions. Of course you can modify it by welding in a baffle extension and extending the stinger pipe deep into the chamber so that it starts where the belly area is, where the exhaust pulse is the most diffuse with the least amount of pressure. (see more info on my site)
What a low powered one speed engine needs is an extended intake and an extended exhaust header to give a broad beefy powerband. I have both types of engines and I prefer this type for normal every day use. I dont even have to pedal from a stop with my 48cc. When I lived at high altitude in a hilly city I preferred my 55cc with reed valve and torque pipe for maximum hill climbing power. But still, a 55cc with extended intake and exhaust has more torque taking off from a stop.
I regret that people spend good money on expansion chambers that are designed to create a very loud exhaust note. They do that by having the stinger begin at the end of the last cone where the exhaust pulse has been concentrated down to the smallest size so that it has a higher pressure. That high pressure exiting the stinger (or the silencer) creates more noise because of the greater pressure difference between the exiting pulse and the outside air. That is my first gripe. Second is that they reduce mid range power in order to increase top rpm power by means of a steep angled baffle cone, which is a design only beneficial to racer engines with transmissions. Of course you can modify it by welding in a baffle extension and extending the stinger pipe deep into the chamber so that it starts where the belly area is, where the exhaust pulse is the most diffuse with the least amount of pressure. (see more info on my site)
What a low powered one speed engine needs is an extended intake and an extended exhaust header to give a broad beefy powerband. I have both types of engines and I prefer this type for normal every day use. I dont even have to pedal from a stop with my 48cc. When I lived at high altitude in a hilly city I preferred my 55cc with reed valve and torque pipe for maximum hill climbing power. But still, a 55cc with extended intake and exhaust has more torque taking off from a stop.
