Mr Skyline Man - i will repost something just for you.
Let’s sum this up in a simple chart to visually explain how this works:
2 stroke engine (up, down) – 1 complete crankshaft revolution.
4 stroke engine (up, down, up, down) – 2 complete crankshaft revolutions.
6 stroke (rotary) engine (up, down, up, down, up, down) – 3 complete crankshaft (eccentric shaft) revolutions.
If its a 2 stroke engine then it only expells 1.3l. If its a 3.9l then its a 6 stroke. So one theory will cancel out the other, its either 2 stroke 1.3l or a 3.9l 6 stroke. As it is quite obvious that its not logical for it to be a 6 stroke and its perfectly plausable to be a 2 stroke then it has to be a 1.3l. If you want to look at it from the rotor's perspective rather than the e-shaft then you need to think of one rotor being one piston that is able to produce 3 operations at once and able to complete three combustion cylces in one rotor revolution.