Even though the window is attached there is still a large wake from the beltline down. I am going to build it as long as possible while still fitting the license plate and tail lights on the rear surface. With 15* angles the skin friction should not be a problem, and wake reduction will be significant- perhaps a mere fraction compared to stock?
Remember, the stock Cd of this car is something like 0.30 or 0.31. Not spectacular- there's plenty of room for improvement. With a basjoos style nose cone it should be even better. With the full belly pan, boat tail and low nose I'm expecting something like 44mpg sustained 60-65mph highway cruising instead of about 38mpg now. That's a 16% FE increase, or 32% aero improvement.
The goal is to get low 40's without P&G'ing everywhere. It gets old, especially on long trips. I want to go to Duluth and back on $30 and when I have a girl in the passenger seat I'd like her to not be mad at me.
Also interested in what you're thinking for "mechanical improvement"?
WAI could come in the future if I can bribe someone who knows what they're doing.