Actually Ken, that is the only time it matters is when comparing work. Work is defined as the amount of energy extracted from the working fluid per unit time. To figure out what this is you must look at the full cycle and how many of them occur per unit time. Otherwise the comparison is meaningless. I promise----follow the fluid. Ignore the hardware. Crank shaft degrees are meaningless. Like I said measure the displacement of your 302 via the cam drive---it becomes a 604 or if you prefer a 2 cycle 302. 2 cycle, four cycle, number of equivalent cylinders and numbers of eshaft rotation all can be arranged to get the right mass flow, but you cannot analyze the engine this way from fundamental principles.

 

Don't make me draw a PV diagram!

 

Monty 

 

 

 

 

None of this matters if you are COMPARING the WORK of the typical 4-stroke with the WORK of the rotary.  This means by definition that you MUST find a common means of measurement of that WORK.  The only place that this takes place is at 720 degress of crankshaft/eshaft rotation.  At 720 degrees of eshaft rotation the rotary displaces 2.6L.  If you aren't trying to compare the 2 engine types then 3.9L is correct for the rotary since it rotates 1080 degrees in 3 rotations of the eshaft to WORK all 6 faces of the 2 rotors (but this isn't a valid comparison to a Lyc or Chevy!).  Ed A. had it right earlier even if he did change his mind.

Ken Powell
Bryant, Arkansas
501-847-4721
C150 / RV-4 under construction