I talked to one of my buddies on the phone after reading your post. He told me that I may as well design a super flat and smooth bellypan with a "raked" design (Duh !)
He told me that the bellypan should go straight but have a 5 degrees or a little more slope upwards (max 8 degrees and thereafter you have a violent turbulence) so the air passing with high speed and low pressure will discharge upright and smoothen out the turbulence behind the hatchback... He also said that a couple of deflectors here and there would help too...
I don't know; I guess I will be using corrugated plastic or polycarbonate sheeting... I believe I will design a diffuser at the end of the bellypan so I get rid of the turbulence which "grips" the car' s tail...
Lemme see what we can do...
I am aiming to design such a combination that it will be :
I acctually would have loved to go buy a second hand to experiment on it but I do not think I can afford it right now... I have an average of 35 to 40 mpg but when I give it a push, I easily exceed 25-20 mpg. I never imagined a 1.4 could burn so much !
I plan to name this black beauty' s name as "Dark Magic" or a corny name alike