johnny99 wrote:There seems to be a large enough radius at the front, which may give a bit of drag, if that was to replaced with a sharper edge, it may lower the drag at the front.
The skin friction drag due to accelerating the air over a more curved surface near the front is really negligible in the current design.
The biggest sort of drag you can expect from the shape as shown is the vortices generated from the air spilling detaching at the sharp angle at the sides near the front, and similarly at the back. It might be worth taping some threads on the car and see where the flow detaches.
For this reason, it might be worth extending the side panels near the front and the rear a bit in order to create fences to better direct the air over the car, but again, just how far to go with that isn't easy to figure out.