Brian,
thanks, I'm very interested in this topic.
The Plus 8 has a relatively unusual combination of a steeply sloping flat rear deck panel, which seems to develop a vortex as air is blown up into the downward facing louvres, and a flat underside that slopes slightly up from the rear axle line. Where they join is essentially a straight line.
Your car has the number plate below the car, which will serve to disturb air flow under the car, others have it above which will disturb the flow over the rear deck.
So, does the rear of the car produce lift or downforce? Both are possible! If there is lift then I do wonder if an F1 style rear diffuser would help. This is an interesting article...
Diffueser So, yes if they have any data it would be interesting, as would the "under wing bits"....
