Actually what's interesting is the accident didn't take out the bumper at all. Had Ventureshield on there to protect it from minor bumper hits in parking lots (because no one here will leave a note if they hit you, especially if it's an expensive car). Bumper didn't even have a scratch from the impact. Ventureshield was completely taken out though so I can attest to the fact that it works for a 100 kmph impact!!
Anyway just finishing up the fabrication drawings for the factory.
Decided not to go with the smooth underbody. BMW has already installed an underbody panel system to smooth out the underside and the only exposed areas are the exhaust system and the rear differential. So my underbody will cover the rear differential area and rear bumper area which builds up a lot of turbulence. It'll keep the costs lower again.
Designing an optional frame system with fins though to channel the air through the entire underbody to the back.
And yes, testing it will be difficult. Everyone's setup is different and it depends a lot on the ground clearance too (which changes depending if you have your car lowered or not). Also, the main issue is finding a wind tunnel big enough to put a whole car in... there is a wind tunnel in London (
http://www.vigyan.com/capabilities/wind-tunnel1.shtml) however the test section is 3'x4' which is way too small for a full-scale test. Most wind tunnels are usually pretty small because they're used to test a small section of something like an airplane wing and not really for a whole car. When I was in school, we would build scale models of bridges to test the hydraulic effects on the piers and then factor our results for scale.
So...what I was thinking of doing actually is trying it on a 1:18 scale model. I'll build a 1:18 scale mockup and just tape it onto a 1:18 scale model. I'll use load gauges to measure the change in force on the wheels. If I had access to a full scale wind tunnel, my setup will be the same (load cells under the wheels).