Stupid Idea
 

If you could get some highly polished (internally) tubing of e.g. 6 inches diameter, why couldn't you:

(1) Have an open grille, with all airflow going through the engine, then into the 6-inch tubing
(2) The tubing then goes from front - back of car (if somehow it could be hidden)
(3) The tube opens in the middle at the back of the car - into the low pressure drag area.

The result is that the drag at the back actively removes air from the engine bay.

Benefits.
(1) The grille at the front reduces the total airflow around the vehicle
(2) All airflow through the engine doesn't go under the car, so drag there is improved
(3) The drag area at the back of the car ends up being closer to atmospheric pressure, so drag is reduced.

This could be done in a custom EV (in fact, in my plans for a prototype I made, this has been designed in).

Any comments? :)

Is this part of the purpose of the side scoops and such we see on mid/rear engine cars? It makes sense, but hiding the tubing would be difficult...have you checked out the bottom of your car?

BMW had something similar for the brakes, and there's a pic showing the airflow through the rain tray and out the back sides of a VW....

It's a valid idea. GM's PNGV Precept Cd .19 concept car expelled exhaust into the wake. It was also rear engine, though, and active louvers (I think) drew cooling air off the rear quarter panels only when needed.

How much surface area are you funneling down into that 28.27 square inch (six inch diameter) pipe? If the engine bay area is 3 feet wide and 2 feet high (864 square inches) then the air speed through the pipe will need to be 30 times faster than the vehicle's speed. At 60 mph the air speed through the pipe would need to be 1800 mph to not produce any resistance.

to reduce draig you would have alot less work ahead of you if you just removed your passenger side veiw mirrer.