seattletom wrote:
Is anything needed to get air out of the back of the car, like cutouts or louvers in the boot back panel?
If not necessary, I would at least call it beneficial. Cutouts or louvers would work, or a gap between the diffuser and boot...Which is what I typically envision. Another reason for ensuring the air has a place to flow out from the rear, is that you'll probably also be best served to have a constant supply of air flowing around the heat-generating differential. With an LS3, if you have plans to do more than cruising, you may even consider ducting some fresh air into the tunnel (or boot) for this reason as well.
seattletom wrote:
Do the rear axle cutouts suck air in or provide an exit path for the tunnel air?
Probably a little of both, as the area between the front of the fender and the front of the tire should be low pressure, while the area between the rear of the tire and the rear of the fender should be high pressure. Regardless, going through the wheel wells is probably not the easiest way for the air to escape. I'd definitely try to provide an intentional path of least resistance for the air, like the vents/louvers/gap you're already thinking of.
seattletom wrote:
Seems there should be a low pressure area behind the car that could be put to use.
Absolutely there is.