[spacemanspif]

My reasoning for starting the thread was an idea from an observation just under the assumption that the back half of the wheel well traps air and is a parachute of sorts. Ideally, radiused wheel wells would be used like on these club cars with the back 1/3 of the flare cut off. But since paint protection is a concern for most who drive their cars more than 1x a week and not on a race track, I thought the vents would be a good alternative and possibly (if they work like I'm thinking) be a cleaner, better looking alternative to wheel skirts. Skirts would be ideal but some aren't willing to take the plunge so if you could add a vent and get 75% of the benefit as making a skirt, it could be worth it. I'm guessing that the larger the space between tire and wheel well, the more air is trapped and the more benefit could be had from wheel well treatments of all kinds. Flared fenders like those on STIs and VW beetles would be easiest to do it on, but some creative ducting could be used to adapt to any vehicle much like how BMW did it with the aforementioned vehicle.

In regards to the Jeep comment, large fender flares will catch a lot of air but to cut off the last 1/3 would mean all sorts of debris from the tires getting kicked up and hitting the body and possibly the driver. Cutting an opening and attaching down facing vents or a small-ish screen could prevent body damage while alleviating some parachute affect of the flares.

On engine cooling: those with full belly pans have to exhaust radiator air/heat somewhere. I've seen a few that do it into the front wheel wells. If the pressure in the wheel well is high, then it could prevent some cooling as the max amount of air isn't being allowed over the rad. Venting the wheel well at the rear could possibly help maximize cooling as well if it drops the pressure substantially, Right? Otherwise a fender vent connected the engine bay would be needed (assuming the engine bay is completely sealed off)