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