Exhaust design By captonzap (Read 737 times)

[captonzap]

Has anyone experimented with exhaust enhancements on the 50cc 139QMB engines? Not the "I'll buy whatever I can get" kind, but more the "what happens if I increase or decrease the head pipe diameter, and the length", and then the expansion chamber size and shape, the effect of megaphones, w/wo reverse cones, perforated baffles, etc.
Do they race 50cc scooters, and where would info for that be found?
Thanks, CZ

[nulldevice]

I cut off the stock muffler and brazed a 3/4 inch pipe coupling to it. make sure you get past the restricter welded into the muffler end of the header pipe that may be in the pipe. Mine had one. Buy a bologna shaped muffler for a Briggs and Stratton 8 HP motor, the one with the male 3/4 inch pipe thread. The power increase was phenomenal, my speed going up steep hills increased by 20 to 25 percent. I also put a free flow filter on the carb and increased the main jet size until it got too big and then backed off one size. There was not much top speed gain.

The noise was a bit too much for me so I brazed a second B&S muffler to the first one. I lost some HP but the drop in noise was worth it, and still much better performance than stock. If I did it again someday I would invest in some ear plugs.

[alleyoop]

Null, you crazy nut(HAHA), yea don't go deaf on us will you
Alleyoop