[Keith Seymore]

My answer would be: it depends.

Aero is a funny thing. It's not always intuitive and you really never know unless you "smoke it" in a wind tunnel, or in some other way test so that you can visualize it.

We decided one time to remove the parking lamp on truck and replace it with a cold air inlet for the engine. Didn't work at all.

When we smoked it in the tunnel we immediately saw the air was hitting the inboard side of the inlet, shooting across the surface and coming right back out the outboard side of the inlet. No air was going IN the tube. Totally not intuitive.

Similarly, on the Volt program, we would add all these little "skegs" that could be worth one, two, three, five "counts". The problem was that while you were consciously making changes on one end of the vehicle you could be unconsciously making changes on the other end of the vehicle of similar or greater magnitude, polluting your results.

My summary is the same as Tom's: if you add a small air dam that forces air through the radiator and into the engine compartment = worse. Better for cooling, but worse for aero, because all that air is getting trapped like a parachute in the engine compartment and would need to be adequately vented.

If you added a large air dam, under the bumper, that forces air around the vehicle instead of under it: better. It would be similar to adding smooth body pans to streamline the underside of the vehicle.

K