Randy,

Is there some general rule for expansion chamber muffler volume? Like x times cylinder volume or something along those lines.
I think we can optimize it (or all other chambers too) acoustically but will that be the best for stunt run, difficult to say.

Lauri

Hi Lauri

Yes , but it is not as simple as that, the formula has to take in not only volume, but  exhaust EXIT  size, and  then you need to consider baffles and how free or stopped up the muffler is
If you use quiet baffling inside that hinders the flow, then you need to be 18 to 20 times the swept volume of the engine as opposed  to free flowing  at 10 times engine volume
The exit figures in this, for example  using a 60 to 65 size engine  the exit should be .350 to .400  inch , make it smaller, you will need more volume   larger and you can get by with less volume.  THe exit on the muffler  should "normally"  be  2 to 3 times the size of the venturi (open area) . although this can vary depending on other factors, and I know you want a Quiet muffler.
Let us take a 75 or 77 size motor,  I would start with a  .190 to .200 venturi , this would make for a .380 to  .400 size outlet in the exhaust, or need to go larger  you could use  2 exits  at .250 to 300  each, this would be quieter than a single  .600  size,  This setup would  work with a quiet baffled  muffler.  Just keep the baffles  free flowing  without  tiny passages in them, and its best to change the direction of the flow as much as possible , such as something like angled 1/2 - 3 quarters  baffles

If you have other specifics I will  address  that size, just send the numbers

and  I have to add, the  pipe, with way more  expansion area  is  even better, and with the expanding section, scavenges  very very well, far better  than any muffler you can make  while still  keeping  quiet


Randy