Does anyone have info on muffler design criteria.. I need to fabricate my own system for a custom setup. I need to know how to calculate what the inside area for the header and can need to be, exhuast tube outlet size and best location for the pressure nippel, and anything else I need to know.

Thanks in advance for any help you can provide,
Randy

It is very complicated, and needs to take into account quite a few variables.
without study, use the cut-and try method, where the header diameter surface is 10% larger than the exhaust port, the stinger has the same size or slightly smaller than the carb, and the first chamber volume is 12 times the engine capacity.
Then do a study on mufflers and see to improve muffling/power. That may keep you busy a while

hehehe So true.

Thank you this is very help for what I need. The 12 x engine capcity seems to be large.. if you check the area of after market mufflers such as slimline they come no where near that size and work great. Even the stock muffler would not be that large by my calcs. I used this formula: Pi x r sq. x length to calculate the volumes of the stock and aftermarket mufflers I am now have. The engine is a .91 Cubic inch. so 12 x .91 =10.92 cu/in My slimline that I am using on my other 91 is 3.6816 cu/in and the engine runs great.. a bit rough in the mid range but great high and low idles with excellent transistion.

Best regards,
Randy

Sounds as though you are ready to go ahead and make your own muffler already without our help?

http://www.macspro.com/tuning.asp

http://www.rcuniverse.com/forum/m_42...tm.htm#4226613

http://www.rcuniverse.com/forum/m_36...tm.htm#3631654

http://www.rcuniverse.com/forum/m_31...tm.htm#3191124

http://www.rcuniverse.com/forum/m_22...tm.htm#2202637

http://www.rcuniverse.com/forum/m_43.../tm.htm#432974

Not at all, but good research means investigation...It is possible that there may have been a typo. So I did the math and compared to a known and they don't jive. I think that would be a good reason to question the math. I understand that the manufacture may have derived their dimension from exhaustive (no pun intended) testing that may not follow a rule of thumb equation. Consequently I need more information. I do not plan to build the muffler, but am working with a custom muffler builder. His size for the chamber was 3" x 1" alum pipe being fed by a 1/2 " x 1"header and 2 3/8" exhaust pipes. The formula agrees with the header and the pipes but again the chamber is much smaller and this concerns me. This seems to be true for every one of the 13 planes I have flying, maybe the formula I used is not the correct one for volume of a cylinder?

Regards,
Randy

Apparently the mufflers you have been measuring were made without significant consideration of the internal volume?

If you know that one works pretty good copy it.

If you want a tuned muffler, you will need to do some reading like the links I sent you.

I would not call their efficiency great. I do call their construction convenient though they play havoc with the engine performance and temperature.