Structural role of the rear box sections?

[firehawk]

Wow, thanks for the excellent information! I hadn't really put as much thought into underbody aerodynamics as I probably should have. So far I've only been thinking about a rear diffusor-like thing which would guide air away cleanly, instead of making turbulence on the fuel cell, swirl pot, diff oil cooler/pump/filter, whatever stuff I have there.

Quote:Reduce the amount of air flowing under the car. : What doesn't get under the car, doesn't get to push it up..easy as pie. The way to do this is to get a lip spoiler as low as you can get it. ...
Smooth undertray: Once you get the air under the car it makes sense to have as little restrictions as you can..

The TRD N2 kit has actually a very nice front lip which extends quite low and includes small intake holes for brake cooling ducts. On several photos I've seen of N2 cars, an aluminium sheet has been attached to the underside of the lip - I don't know how far it extends back from the center. Most probably not further than the front crossmember. It also has the additional bonus of shielding the lip from getting damaged when taking the apex a bit too far over a curb.

As for cooling the engine bay, maybe I could use two small NACA ducts on the undertray just behind the radiator diverting air in and two larger ducts on the rear edge of the bonnet mounted shallow end rearward to exhaust air both coming through the radiator grille and the two small ducts. The air passing over the bonnet should create a low pressure point on the duct's ramp and help to pull out hot air from the top of the engine bay. Some cars also seem to use those large "drop vents" on the center of the bonnet.

Quote:Wheel wells: Again the wheel wells catch a lot of air that cannot get out. You could think about running ducts from the rear of the car to the rear wheelwells, allowing air trapped there to escape.

This I hadn't thought of at all - excellent point! Cutting the rear corner boxes actually helps a bit as it partially opens the rear wheel well all the way back to the rear bumper. After this, cutting holes to the rear bumper would allow the air to exit. Of course, the top half of the wheel well is still closed at the rear but because the N2 flares deflect the air quite well, most of the air coming into the wheel wells probably come from underneath the car. Small vertical "walls" along the rear frame rails might also aid in directing the air from the wheel wells and isolating these air flows from the main airflow along the "diffusor".