engine's cylinder fires only once every two revolutions.
's cylinder fires every revolution, so a 2-stroke has (all things being equal) double the output for the same cylinder size.
Problem is that 2-stroke petrol engines don't scale up in size well (though some industrial Diesels *are* 2-stroke).
fires (like the 2-stroke) once for each revolution, so it has potentially twice the output for the same volume as a 4-stroke, plus the rotary *does* scale up OK.
Piston engines absorb energy during the compression cycle, giving a negative torque, but rotaries provide positive torque for each entire revolution, since compression, power and exhaust occur simultaneously.
Rotaries can run to very high rpms compared to piston engines because their motion is continuous rather than reciprocating and because the few rotating parts are small-ish and can be made very robust, while piston engines are limited to lower and lower rpms as they scale up.
Rotaries are thirsty if you cane them, but I get 30 mpg touring at 70 mph in my 1985 Series 3, no mods.
Fuel consumption is an issue - it's to do with the combustion space being a long, thin rectangle, rather than the more ideal cylindrical space of a piston engine.
And having a turbo giving over 270 shaft HP from a 1.3 litre engine has got to be a temptation....
But no, NOTHING else in the car park looks as damn sexy!