Generally speaking . . . how 'hot' IS the exhaust from a Wankel engine? If a Wankel exhaust is 'hotter' than exhaust from a piston engine, how 'cool' is exhaust from a piston engine?

Also, is the exhaust temperature of a piston engine relatively the same for 4 cylinder engines and 6 cylinder and so forth. Or is the exhaust temp of a 12 cylinder 'cooler' or 'hotter' than a 4 cylinder?

(I don't understand [maybe thermodynamics is involved here] how a Wankel rotary and a piston engine [both being internal combustion engines having, roughly, similar compression ratios and using the same fuel] can have different exhaust temperatures. What properties cause the Wankel exhaust to be 'hotter'?)

 

it's generally because of the differences in the expiratory path ways: in a wankel-type engine, you've just got this huge hole in the side of the block that the gasses fly straight out of, immediately after combustion. with an otto-cycle piston engine it's the amount of conductive material the gasses pass around on their way out (head and valves mostly, but spark plug, piston face, block are still good conductors) which makes the biggest difference, with another whole stroke to push the gasses out of the combustion chamber (allowing conduction to happen over a longer period of time).