Here some sketches of my latest reasearch of underbody aero I never finished completely.
In principle I have studied more of the golden years of downforce (ground effect cars) 1981-83 when many things were still ok for FIA before continuous limitation of underbody tunnel structures.
I figured out for my small understanging some differences between 'single wing underbody' and 'double wing underbody' (like in 956 prototype and first versions until forbidden in FIA C-group series) with a air wave under the front body:
I understood IMSA and some other series also adapted to that doublesail arrangement (some kind of borrowed sketch of suction power under the car with different arrangements:
Norbert Singer said about 956 that the downforce and grip of the front part in 956 was almost completely adjusted through alterations and adjustments of the aerodynamics in the rear end, which tells lot about the characteristics of upside down wing car.
The massive tunnel under early 956:
The underbody of Ferrari Enzo:
This is where I have got after some studies. Now as the green 911 is finished for the following season, I have plenty of time to build this underbody arrangement: front and side parts fiber structured, centre plate aluminum, rear diffuser fiber + aluminum structure.
My aim is:
a. to get rid of slowing rear wing when getting also rid of the lift of rear in over 270km/h speeds this car has now without rear wing.
b. create better grip to front to be able to drive through very fast corners with less need to add grip to front with soft left foot braking when still flat out and pedal in metal.
This means that the major point to create more ground effect is located under the centre of the 911 rather than under thre rear of the 911. Therefore prior to underbody structure is fast flow under the seat of driver, when the function of rear tunnel / diffuser is only to be best possible to create more acceleration for the air escaping from under middle part of the car and it isn't therefore that precise of its laminar capabilities rather than centre of car is.
If developing similar system under my becoming racing 928 (slow progress shown in other thread) the centre point for needed ground effect would be little bit more towards the rear end than in 911.
This much for now. Progressing...
