My attempt at an air dam (1977 MG Midget electric)
 

I built this air dam for my midget to see if I could improve it's range. I've been keeping data on my regular commutes, and specific runs at 50mph and 60 mph. It was easy to build, and I've added an article on my site about how I built it if other want to try this. For me it didn't show much difference. Maybe 2.5% reduction in drag at 60mph. The Midget has a clean underside with nothing really hanging down. It does have holes up into the engine compartment, so I was hoping it would help, but I wasn't surprised it didn't. I'm getting good range with the car, but I'm always looking for more. I measured 112 miles on a single charge. You can see this at my site www.electricmgmidget.com
http://www.electricmgmidget.com/imag...0Finished2.jpg

Have you considered a adding a splitter at the lower leading edge?

I know people think it's just for adding downforce, but I think it's works to keep air from going under the car too.

Project Import – S2000 Front Wind Splitter “Backyard Aero”
http://projectimport.com/wp-content/...2/Splitter.jpg

Nice detail photos you have provided - cool.
http://www.electricmgmidget.com/inde...ing-an-air-dam
http://www.electricmgmidget.com/imag...0Finished5.jpg

Since I saw virtually no change in my drag numbers I probably won't pursue the air dam idea any farther. I might consider adding some covers to the bottom of the car, but like I said before the bottom is very clean now. I'm thinking that once the air starts under the car it stays smooth since nothing is hanging down to disrupt it. I have added tar paper flaps under the rear axle to keep the air going past that, and I don't think that helped either. It is a cool idea in that the axle can move up and down without ripping the tar paper, so the bottom stay relatively smooth even though the suspension moves. One nice thing about an electric car is that I can measure the power used through my controller. It can log volts, amps, RPM, etc every .2 seconds. From that I can compute power and speed. The hardest part is trying to hold the speed constant. Any slight acceleration shows up in logs as additional amps. Also driving on what you think is a level road changes the power values drastically. Very slight uphill or down hill sections show up as huge changes in power at a certain speeds.