Partial kamback on flat back?
 

So I was considering doing a partial Kammback on my van (95 astro van) and I was thinking and I realized that most, if not all, I could find as examples are on cars where the end connects to the bottom of the hatch glass area.
If I follow the template would it still get me noticable fuel economy?
Would the flat back not matter at all?
MetroMpg:
http://metrompg.com/posts/photos/aer...ail-rear-z.jpg
AndrewJ:
http://i239.photobucket.com/albums/f...r/IMG_5236.jpg
What I was thinking: I didn't try to get it accurate with my painting :)
(see thumbnail)
My question is how much would it help for a vehicle with a flat backend?

I can't say I have seen a kammback on a flat-backed vehicle before. Usually people go for a full on boat tail, or a base plate.

Attachment 20748

If you follow the template, you probably will see some gains, as almost anything can improve what you have already, but I couldn't begin to estimate them.

I would assume that if you make the kammback, that the air going underneath the car is going to start doing weird stuff at the back. The air on the top will be lead down, but the air emerging from underneath may just continue rearward. I am going to guess this would create extra lift, and drag (not more than stock, mind you). So if you make the kammback, try experimenting with a rear diffuser.

Your Firefly is Beautiful!

A sharp edge can also be effective giving the air a clean separation point. I'd look into keeping the air out from under the van than at the rear for now, boxy vehicles aren't that bad in the aero department assuming attached airflow is regained along the length of the body.