Originally Posted by Cycofast
So I realize that I'm relatively new to the world of motorbicycling, but I'm fairly well grounded in thermodynamics. What I'm getting at is removal of the muffler on my chinese kit engine to maximize efficiency. The only down side that I can think of would be the ridiculously loud noise as I roll down the street. If you think about it, this might a) create awareness for cars and b) make my bike sound like a real motorcycle. Of course there is the Police factor, but we'll cross that bridge when it happens.
Also a straight pipe exhaust may be an alternative to no muffer at all.
As others have pointed out, if your engine is a 2-stroke
, it needs a muffler. The muffler actually helps the exhaust get out faster than it would otherwise, believe it or not. You would be wise to look around for topics about 2-stroke muffler tuning and mods. Tuned 2-stroke exhaust pipes/mufflers start out thin, flare out to a fat section and then reduce down to a thin section again.
Engineering Acoustics/Sonic Supercharging of 2 Stroke Engines - Wikibooks, collection of open-content textbooks
If your engine is a 4-stroke
, then yes, you can run it with just a short straight pipe, or even no pipe at all--just exhaust blasting out the cylinder head opening--because 4-stroke engine use the piston to actually push the exhaust out. The muffler on a 4-stroke may slightly increase flow (on a multi-cylinder engine with a properly-made exhaust header) but mostly just reduces the noise.
Do note that the vintage board-track cycles had the pipes to guide the exhaust away from the riders' legs