from theory ...exhaust gas might same as intake air, if the ex. gas was cool mean higher density, can b increasing the amount of ex.gas to flow out to the exhaust system, mean exhaust gas can flow out more faster than when ex. gas was hot, agree ? if wrong pls correct . keep discuss on this, quite interested to know about this 

for my point of view, ceramic coat or thermal wrapping to contain the head inside is bcos to avoid the heat to affected the intake air temperature.  expelling heat will increase the engine bay temperature, i'm agree on this, but just for when the car is stop there n not moving.
cos if i spray on the radiator or condenser...it help to expelling the heat also, even i'm not spray it on the extractor,  once the radiator fan working...all the heat will suck into the engine bay also, engine bay temperature will increase also.

hv another way to do on the thermal wrap, that i found out on those custom chopper builder, take the thermal wrap to do ceramic coating. but this kind a costly move also hehehe

if any1 hv more information on this, pls share it here n discuss together. thanks