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Frank, you are misunderstanding what I'm saying. I'm not saying that the flow inside the engine compartment has no effect, but that the only effect it has on aerodynamics is the resistance to air going into the grill. That resistance could be equivalent to a 50% closed mesh, or a 75% closed mesh, but a rear block is equivalent to a 100% blockage of flow.
Your links don't refute that at all. I also stand by my statement that we can't know for sure whether air exiting the bottom of the car is good or bad for aerdynamics. It could very well be pulled out by the slipstream if you have a flat bottom. How about putting a cowl flap on your car?
Can you visualize a fan with enough power to suck through ALL the air that can possibly enter the grill? That's at one end of the continuum, and it would create forward force.
A car with an empty engine compartment that allows free airflow is down the continuum-- air can flow freely into it and exit underneath the car or through cowl vents.
A regular car is in the middle and there is more drag from the resistance to flow that is manifest at the grill.
A rear block is at the other end, with zero flow through the grill.
If you really think the resistance created by having stuff in the engine compartment is so high, then it's equivalent to a rear grill block anyway.
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