"Engine Blueprinting" using The Engine Analysis Program Part 4 "The Rotor/Crank Assembly - Timing" The timing of the rotor or crank assembly is really a simple matter if you accept the timing of the rotary valve or crank, which I use and have found work well on Radio Control Competition Models It really doesn't matter the application. It seems that the same open duration and the same closing point works well for RC Models. The attempt is to open the rotor valve while the crankcase is experiencing sub-atmospheric pressure and close it before the piston forces part of the crankcase mixture out the exhaust. I think that using a total OPEN duration of 215 degrees seems to adequately supply the engine. The point where the rotor valve closes should be at 65 degrees ATDC. You may stretch this to 70 degrees ATDC and you will slightly add to the top RPM of the engine, with a slight decrease in mid range power. I use a closing point of 65 degrees ATDC on ALL my engines and a total OPEN DURATION of 215 degrees. It is VERY Easy to make these changes, if you use The Engine Analysis Software. This program converts all measurements to linear, and you NEVER have to use a degree wheel! I use relatively high timing of the exhaust (183 degrees - 21's, 185 degrees - 45's, 185 degrees - 67's, 185 degrees - 80/90's) and relatively low timing of the intakes (126-129 degrees - all engines). With these timing numbers for the exhaust and intakes, the rotor/crank duration and closing point seem to work VERY WELL! Another FINE source for any serious 2 cycle engine builder is a book authored by Dr. Gordon Blair, a researcher and one of the foremost 2 cycle experts in the world. This is the ultimate technical guide available. The Blair book & software can be purchased from SAE (Click Here