This is one of those endless debates that never reaches consensus, probably because people won't agree on what constitutes a "cycle."
A "cycle" is very easy to define. First observe a charge of intake air enter the engine, then follow that charge as it is squeezed, banged and blown. When that same cylinder or chamber begins to draw it's next charge of intake air, the engine has completed one thermodynamic cycle.
The logic that says the 787B's engine is equivalent to a 7848cc four-stroke piston is the same logic that says a 500cc two-stroke is equivalent to a 500cc four-stroke. Everyone knows there's more to it than that, and that for most purposes, it's an invalid comparison.
Who is this "everyone" you mention. Its certainly not the same "everyone" I know. Certainly 2 strokes and 4 strokes of equal capacity can't be rated equally for performance just the same as NA vs supercharged engines. That doesn't invalidate the method used for determining displacement. Unfortunately when Mazda originally published the displacement of their rotary, they departed from the correct method - nobody noticed at first - and now it's easier for everybody to live with the error.
It's equally invalid, for most purposes, to say that the 787B's engine was comparable to a 2616cc four-stroke piston engine or to say that it's comparable to a 7848cc four-stroke piston engine.
Well its displacement is the same as any positive displacement internal combustion engine that displaces 7848cc. Its cycle is 4 stroke. It's performance is different. It would probably need some help and probably couldn't compete with piston engines bigger than say 5,000cc. So perhaps a 1.5 equivalence would be a reasonable starting point. Hard to say because Wankels are very light and compact for a given displacement which would help compensate for their specific power disadvantage.
If you compare the number of power strokes per crankshaft revolution, a one-rotor Rotary has the same number of power strokes per crank revolution as a two-cylinder four-stroke piston engine, or a one-cylinder two-stroke piston engine.
The crank revolutions of a Wankel are pretty much irrelevant since there are gearing issues.
However, the FIA equivalency formula rated the 787B's engine at 4708cc, not 5232cc. I believe this is because the real controversy is in how to calculate the displacement of one rotor face's power or intake stroke. It's not as simple as in a piston engine where you calculate the area of the piston face times its stroke, because the whole chamber is moving around the rotor face and changing shape and volume during the power and intake stroke, like if both the cylinder and the piston were moving relative to the crank in a piston engine. Rotor face times stroke is not equal to how much air the thing actually sucks in in its intake stroke.
It is actually. There is a simple formula for Wankel displacement. The only conjecture is whether the displacement should be applied to each rotor once or three times. The only logical method is to apply the displacement to each chamber. The Wankel principle can be used to make an engine with other numbers of chamber on each rotor - four for example. Such an engine would displace 33% more than a 3 lobe Wankel and would have an obvious displacement advantage.
I don't even know if the FIA measured that when they came up with their equivalence, but somehow they came up with a 1.8 factor, not 2 or 3. But I'm no expert here and am happy to be corrected and/or taught.
The FIA equivalence factor is an arbitrary number which was hoped would produce reasonable parity in competition. Pretty much like the equivalence factor for supercharging which has been set at everything from 1.4 to 3.0 (and probably beyond) in various forms of racing.