I do not want to offend anyone here, but why would you run a gas engine without a muffler and tach it, then compare it to another engine?. That is not a realistic test. One engine may run better and more RPMs without a muffler. But be realistic are you going to fly your plane with that motor and no muffler?. If you are going to compare RPMs, Use a muffler for a realistic situation.
Who flys without a muffler. If you are going to test and compare engines , test them in a realistic situation. Maybe the engines work better with stock ignitions? What does the motor do with the muffler?. I have a DA 50 and I live at 3000 ft. I know guys who fly 18 lbs planes with a DA 50s and they have unlimited verticle. I have unlimited verticle at half throttle on a GP Wagstaff. I know guys who fly 17 lbs planes with G62 and do they have unlimited verticle?. No. They say they wish they could put a DA 50 engine in there planes but cant because they need the G62 for nose weight up front . Not putting down a G62 but the guys I know would really like to put DA 50s in there planes. And it is not about money because these guys fly $3000 airplanes.


My test results of DA 50 Tach meters, Futaba and TNC

22X10 Mej 7200 rpm
22X8 Menz "s" 7300 rpm
24X8 Menz "s" 6400 rpm