At 09:32 PM 6/12/2016, you wrote: >That equation has never worked for me either.
++++++++++++++++++++++++++++++++++++++++ The only way the equation can be in error is if the "inches of pitch" on the propeller, as stated by the manufacturer, doesn't actually relate to real world performance which it sounds like it doesn't. My prop is somewhere between a 64 and 68 pitch. It started as a 68 and was reworked to a 64 but I couldn't tell the difference. At 66 inch pitch and 2600 rpm, the rpm I ran the race, and 100 percent efficiency, my speed would be 162.5 mph. I was timed at 163.8 . It seems to be a good rule of thumb if nothing else. Larry Flesner
