[basjoos]

One unanticipated side effect of reducing my car's Cd is that I have reduced the pressure of the high pressure zone at the base of the windshield low enough that the remaining air pressure there isn't enough to move air through the air vents without having to run the fan. So which is the more energy efficient way to ventilate the interior? Run the fan on low with its slight load of the alternator, or install a small air scoop somewhere around the windshield to catch and direct air into the car's interior, resulting in a slight increase in Cd. Of course with the latter, I'd have to design it to separate out any rainwater that the scoop might catch, so it doesn't rain inside the car when driving through a heavy downpour.