[Gealii]

The air dam is meant to keep air from flowing through low hanging items. ie. suspension, axle, oil pan, etc. so it can flow under as long as the airflow doesn't attach to pieces underneath.

as far as a grill block from best to worst as far as aero. I could see all 3 being equals as far as warm up
1) on leading edge. This creates a smooth surface to flow over or around the vehicle.
2) In front of grill. It creates a bubble of air that allows the air to flow over but air would still escape around edges.
3) behind grill. This is the most stealthy but air can now cycle around the grill creating a small amount of drag.