Quote:
Originally Posted by Vekke
There are optimal angles but everything affects to the results. First you should decide will you begin your diffusor before or after rear axle. If I remenber correct,
Before rear axle the optimum angle was 3-4 degrees
After 6-7 degrees
Max is about 10 degrees and after that you make lots of downforce
Please correct the values who have the huchos book on their hands...
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Hucho shows 3deg as best for Cd reduction for those with a "longer" diffuser (Cd changed by 0.025), and 4deg as best for Cd reduction for those with "shorter" diffusers (Cd changed by 0.020). You will continue to gain more and more down-force (at least up to 11deg) as you make the diffuser more and more steep. Even up to 11deg, you will have better Cd than flat.
As was stated above, you must have good flow coming in to get good flow going out, so belly pans are your friend. Also, Hucho does not discern between sedan or station wagon, it's just for an underbody.