Bob and Ferocious,

Just took a look at MECOA's site, to get an idea of the mufflers they now feature with their various engines.

I know the 40** (4011, 4050, 4060) engines are loud when unmuffled, and that the older straight tubular can mufflers with exhaust tip out the centerline, not angled out, are also not quiet. The catalog pages also show a new form of muffler, with an aft-expanding cone shaped front half, and a (flat?) rear cap with exhaust tip angled out about 45°. I don't know those.

The stock Sportster .20 muffler is exceptionally quiet: I hope the other three Sportster mufflers do as well. I fly CL only: loudness is less critical than for RC, at many sites. We go no higher than 70' above ground and project a much smaller "cone of noise" over a single point than anything RC except 3D airplanes or helicopters.

Without the stock muffler, my .20 was louder and gained over a thousand RPM easily on the same prop, fuel and day. (I turned a simple spraybar-type venturii to replace the K&B Carb - using the same choke area.) The engine was also easier to hand-start, BTW.

CL Stunt 'tongue', or 'chip' mufflers, do well in the middle of an engine's power RPM range. Load is usually modest, and that's quieter operation by itself. Yes, there is some power loss, but a bit stronger 'throttle setting equivalent' , covers that. We configure "Chip" volume and total outlet area to restrict: no throttle plate or drilled "drum" as in RC carbs. We don't need controllable RPM in flight. A consistent, balanced "single-speed" configuration is most desirable. (RPM does vary in Stunt flight, in response to applying and releasing very large brief maneuver g loadings.) Of course, in CL Scale and Navy Carrier events, throttle is essential. Racing, Combat and Speed events are all "single speed" matters, too.

"Chips" are louder than effective large mufflers, as on the K&B Sportster .20. Stock OS FP and LA mufflers are fairly quiet and serve most of the engine's RPM range.. E.g., the stock OS FP 25 muffler gave the effect of a broad range tuned pipe well up towards the engine's ultimate peak HP RPM. In stock form, a 25 FP (with CL venturii, of course) was a sensible substitute for a GOOD Fox .35 in a "Fox .35 size" model!.

Oh, BTW Bob, one promising possibility for the K&B (or RJL?) .18 BBCL might need throttle - one Class of CL Carrier has a max displacement of 0.36 cu in. Fuel is restricted in some events, and muffled engines earn some extra consideration: stock mufflers in particular. AMA does have noise level guidance, too. Just a thought...