Originally Posted by Euromad
Thios keeps the charge in the crank instead of spitting back through the carb.
For early two strokes this was a great way to broaden the powerband. The exhaust pipes didn't use the exhaust pulses to scavenge the spent exhaust very well. If you look at a modern two stroke pipe it is fat and thin in different areas to make the best use of this exhaust pulsing to suck the spent gases out of the cylinder.
Would it then be inaccurate to think that a rotary valve engine (F7) wouldn't benefit as much from a "performance" expansion chamber as a reed valve or port timed engine? I want to build a low mount expansion chamber for my "street tracker" 175 instead of the high mount stock pipe, but really don't know the first thing about expansion chamber design. I wouldn't want to build something that looked pleasing but it actually hurt performance/power. Then again, I'm not looking to squeeze the last bit of power from the otherwise stock, almost 40 year old engine either.