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The second most mis-understood aspect of combustion engines besides PCV is heat flow.
The engine itself needs to be insulated. It should have thick, cast manifold, plastic intake insulation, blankets, exhaust wrap, coatings, shields, covers. The OEM does more and more of this as the years go on. The temp rise created by burning fuel is your $$$ from that fuel so to conserve the heat and insulate the engine/exhaust is to save money on fuel and get the most from the fuel in terms of shaft power.
Power plant engineering fundamentals always revolve around conserving heat, insulating the power plant, getting the most from the fuel.
If you start ripping that heat away by removing the exhaust wrap and removing the hood (extreme example) you are ruining the engine efficiency, lowering fuel economy and increasing the amount of fuel that needs to be sprayed by injectors to maintain the same temperature steady state.
Its like opening the cover on a propane grill, now you need to turn up the propane gas (fuel) to compensate.
Vented hoods can be used effectively in performance applications, but they should NEVER be used to directly cool an engine, or exhaust system. Those parts need insulation and to be wrapped up tight to conserve energy. Exhaust gas velocity increases as it warms up, it expands and takes up more space (it can move a turbine better at higher velocity, or move to the exit quicker) the hotter it gets.
If you need more info ask questions I dont wana make this into a huge long post
basically the engine bay should be kept cool by insulation, not a vent. Its okay to vent whatever is left but the vent should not be a first line defense.
The radiator needs to deal with the waste heat, and insulation makes sure that all the waste heat makes it to the radiator, and if the rad has trouble THEN you upgrade the radiator, fans, make sure the panels are intact and functional, and finally add a vent to help the radiator as needed.
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