The 1964 "short nose" 2-stroker project have not advanced a bit since my first post here, and I still have not made the slightest aeromod on my 1975 V4. (life has it't priorities) Fuel efficiency have however advanced a lot, as a result of improved driving skills only. The average consumption now seems to flatten out at around 4.6 litres/100km or 50 mpg (US) by extreme "Drive Without Brakes" and "Burn & Glide" with engine shut-off.
I have tried with 7-8% larger tires and noted a 1-2% improvement, but the negatives killed most of the joy. Larger tires should be equivalent to a 5:th gear and should reduce consumption much more, but I guess my driving techniques makes that marginal in comparison.
I think the only way to improve the numbers further, without replacing the stock engine, is to start experimenting with aeromods. A kammback boattail extension would probably make quite some difference, but it's probably also the aeromod with lowest WAF... (wife acceptance factor) I'm therefore thinking of starting with something less radical, an air dam/splitter for example.
The Saab 96 have a flat and smooth belly with few disturbing shapes. Even the engine compartement has a whole floor, except for a square hole just around the oil pan. The lower front edge is slightly rounded but ends with a sharp edge (seen from the side) that I guess will force som of the rammed air to rush below the car as turbulent flow.
Here's a photo of a slightly customized 96 V4 with the front bumper removed:
My idea is to direct all air hit by the frontal area sideways and above the car only, leaving whats below the body untouched. The plan is to make an air dam that drops vertically from just below the headlights, down to the level where it meets the horizontal floor-line. This should direct more air up and sideways instead of squeezing some of it under the car. Since an even sharper edge will probably increase turbulence under the car I will extend the floor-line into a splitter. Such an air dam/splitter will be quite high above the road compared to others.
Since the Saab 96 is unusually flat below, I don't think there would be any improvement by lowering the ride height. I believe it's better to leave the still air under the car than scooping it around.
If I can avoid pressure differences between the belly and the sides I hope the sharp edges between the doors and the floor isn't harmful. Something will offcourse happen around the tires, so perhaps some sort of skirt between front and rear wheels is a good investment anyway? Such a skirt could be made of thick rubber so it won't get damaged over speedbumps etc. Perhaps even a "diffuse skirt" made from a number of brushes/brooms in row can successfully fill this area up?