while i dont agree with lazy on the "ruined" part your wrong about the cowling removing hot air. they are designed to draw high pressure air from the windscreen junction INTO the engine. heat release from an engine bay only occours when there is a pressure difference. because the pressure at the base of the windscreen is soo high, it stops air from exiting, and in cases like the reverse scoop, is designed to utilise the high pressure to force air into the carb.

heat extraction needs to happen at the front 1/3 of the bonnet to be successful without major work to address the pressure differences.