If only there was a kit replica company that could recreate the shape of the EV1, it had somewhere between 0.188 and 0.195 depending on what source I ran into, making it the most aerodynamically efficient vehicle produced. If only it's design could be created again.
I took note of post #10 from RobertSmalls on this thread
So, the EV1/Impact started with a Cd of .188. This drops to 0.167 with a mirror delete, short springs, and some duct tape, and 0.153 with a 16" boat tail.
Impact/EV-1:a forensic reconstruction - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
Post 10 and on has some very good info for you from that thread, also check out the other aero thread that was opened and being discussed right now.
Designing a tail extension for the first-gen Insight - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
...with it's associated thread here.
03 Insight Whale Tail?
