ORIGINAL: pe reivers
I am not comparing with pitts mufflers. They are exhaust gas collectors, not mufflers, and only serve to harm the engine's potential.
the difference between your OS 108 and OS 1.60 should be larger than a mere 10%, and yes, the gas engine will pull about 1 : 1.5 lbs less than the comparable glow engine of same displacement. I have measured 19 lbs pull on my 26cc test engine, using the MVVS tuned pipe.
That is more than enough to adequately hover a 12 lbs plane.
I agree that pitts mufflers are just gas collectors, but it also appears that at least 50% of the people on RCU want to run them--so for practical purposes I think the motors need to be compared like that as well.
I agree that the difference between my OS160 and 108 should be more. My tests show with pitts OS160 pulling 18x6 @8,800 and 18 pounds of thrust and my OS108 pulling 17x6@9,050 and 16 pounds of measured thrust--the 108 does well on a 10 pound 3D plane. The OS108 has a very free flowing pitts that is loud--that may be why it is doing so well.
I agree with you that the MVVS on pipe is good power on a 12 pound 3D plane.