You cant "just ignore" the rotation factor. its the only way to create something consistent and precisely equivocal between the two styles of internal combustion engines. If you want to compare the two engine types, you have to have a constant. What is more constant than the point that transfers the power from the point of generation to the drivetrain?
If you don't want to compare the rotary to a piston engine, then i feel that 3.9l could very well be more accurate in the aspect that in 3 rotations it does displace 3.9l.
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Uh.... hi.
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