It probably does work just fine because it is a high pressure area! I'll be skinning my car soon (mostly just because I like tinkering), but for anything that needs cooling, I'll be doing what Porsche does on the Cayman's flat underbody--scoops that stick out underneath and kick air up over the transmission. Works both at low speed when it's high pressure, and high speed when it can direct air upwards.

 

4 ducts with one facing the opposite direction. I think the large one in the center is for the diff, the two small ones on the sides for rear brakes, don't know about the other one--maybe it's for engine bay outflow. The small ducts were probably originally intended for the rear brakes but they found the diff was getting too hot and had to direct all 3 rear ducts to the diff.

But still a flat bottom is mainly used to generate downforce--low pressure, so air wouldn't flow from under car to whatever is being cooled. It would be much more functional without all the ducts.

 

like i said; initially, i thought those 2 are built for rear brakes, but i was wrong.

however, this flat bottom diffuser is ultimate. the rear lift shouldn't be the issue with it.

 

somehow they need to cool the gearbox too.
maybe front "out" duct is to create an airflow around the gearbox...

 

If I were to run a full flat bottom I'd want tranny and diff coolers with sucker fans pulling from those vents. But that's probably 10k better spent elsewhere.

 

why don't you trust NACA ducts?
they're supposed to be very effective.
but yea - it's all theoretical discussion. not many of us would spend 5K-10K on flat bottom

 

If the flat bottom works and you end up with a low pressure area under the car the NACA ducts would not supply air, they would actually pull air through the ducting to below the car. Using sucker fans would ensure the cooling flow needed and help lower the air pressure under the car. But yes, this is a theoretical discussion because of cost.

 

would it actually be lower pressure than the air around the diff/ etc?
I'm not very knowledgeable about aero but from there would have to be air entering this area from somewhere, but by the time there was a decent undertray there may not be enough opening to get enough air in if that makes sense

Also, I would assume that "low pressure" means lower pressure than other areas of the car rather than lower than ambient air pressure? Or is it actually lower than ambient?

 

No, it's actually lower than ambient. In the CFD pressure plots below, green is ambient pressure and the blue under the car is lower than ambient.

 

overall, this piece seems much better designed compared to pwjdm.