The RPM's are about the same as without a muffler at all.

The exhaust pipe is about 5" long and has and ID of 0.7". That is large and free flowing. The big chamber seems to be acting like a shock obsorber, or "gasious capaciter" if there is such a thing. The gas in the chamber compresses when the pressure spikes. It is then released at a more constant pressure. There might be some resonant effect going on too. The chamber is 15X the volume of the engine's displacement. It has a quiet and pleasing low frequency sound.


At this point prop and intake noise are much more significant then the exhaust noise.

BTW, I am not an anti-noise, annoying type. My fellow club members aren't either. I have run straight pipes without complaint. My club is way out in the "boonies". It was more of a fun 2-hour project to see what happened.