Belly pan + Fan concept?

[Bicycle Bob]

When you want free ventilation, you have to be sensitive to the air. Good ductwork can cost more than fans, and it is bulky, so you don't see a lot of it. The air exiting the cooling chamber won't want to accelerate instantly. It needs a nozzle, or in this case, a flat, tapering duct. Unlike the nozzle in a paint-spray gun, it will only be getting help from one side to sweep the exiting air away and make room for more. Fortunately, if the intake is nicely placed and well-ducted and sealed, there should be lots of pressure difference to help. In planning the belly pan, leave clearance for that air all the way back. It will be a sudden thickening of the boundary layer.

[meanderingthemaze]

Originally Posted by Rokeby

The issue here isn't the shape of the cooling air exit opening. It is the most
effective -- or least harmful -- direction for the air to be moving as it passes
through the belly pan.

That makes perfect sense. You need that arc to ease the angle of airflow into the air traffic flowing under the car.

There is another interesting element in the picture, the vertical air dam in
front of the exit opening. I suspect this is to make a low pressure area
behind it for the exiting cooling air to fill.

Yes, i didn't notice that on first glance. Although it would seem to me that a curved piece would be better than flat in almost any case. But experts please chime in.

[meanderingthemaze]

Originally Posted by Bicycle Bob

Fortunately, if the intake is nicely placed and well-ducted and sealed, there should be lots of pressure difference to help.

So, perhaps it's hard to generalize, but should the exhaust vent be bigger in area than the intake?

In planning the belly pan, leave clearance for that air all the way back. It will be a sudden thickening of the boundary layer.

So similar to the air dam that Rokeby posted? The car is going to be low to the ground in the front, perhaps 6" or less, will that have an impact? Would giving the truck a forward rake of about 6" help or be a good enough substitute?

[Bicycle Bob]

Presumably, the entry and exit holes will be passing equal volumes. Size them according to the velocity you want to match them to. The slicker the bottom, the faster the flow there. A bit of rake is a cheap, partial fix for this and other common issues.