Just ran most of my .40 to .46 motors for something to do, and for comparison. New house is in a settled area, so I wanted to get it over with. I used a Master Airscrew 10-6" prop, 10% Ritches brew half Castor. Pretty hot humid day. Sweat was dripping on the tach. I ran most with open exhaust and mufflers where it was easy to do that. Not sure how to set margins OS SF .46 14,600 RPM powerbox muffler, 15,600 open exh.; OS FSR .40 13,800, muffled (9-7 prop was 14,800, as that was on my little combat SPAD) ; Thunder Tiger Pro .40 14,400 muffled; Old cross scavenged K&B .40 13,500 muffled; LA .46 14,000 slightly opened muffler, 14,600 open exh. OS LA .40 12,600 stock muffler, 13,800 open exh.; T Tiger GP .40 open exh. 13,400; OS FP .40 13,000 opened muffler to only 1/4" and 13,400 open exh. Royal .46 (INC) 14,000 with muff.; FX .46 15,000 with opened outlet and baffle, 16,000 open exh.; Supertiger .45 15,300 and 16,000 open exh. I suppose a pipe might get all the numbers over the open exhaust readings, or Jett muffler maybe. These were just the random motors I picked up out of the drawer. I have doubles of some like the LA .40s which may be better or worse. I guess my fast planes need the Supertigers, or the newer OSs with maybe a pipe or mousse can of some sort.