Engine compartment design
 

In my never ending quest to keep my engine running cooler, I have a plan. But I need to know the reason for the engine compartment vents. Are they to let cool air into the engine area or, to let out hot engine air? The vent I am talking about is actually the grill area on the back lid, closest to the rear window. My car has a tail with 2 grill areas, actually. I am wondering if one lets in air and one lets it out. If we have an air cooled engine, then it stands to reason that we would want as much air as possible to get in to the engine compartment. Is the purpose of the tail that I have for smoother aerodynamics and rear down force? Anxiously awaiting replies on this one.

I think both grilles are to feed the fan.

If you consider the volume of air the main blower moves, especially at higher rpms, it'll be clear that there's no way that any air is moving out of the engine lid vent(s). It comes out down below.

Some tail designs allow more air to go in the decklid vents, others less. But the primary function of the tails is to reduce lift at high speeds.