Using golf ball dimples to decrease vaccuum drag on motor vehicles and aircraft.

[Bararontok]

The best way to compare the performance of a car body with golf ball dimples or vortex generators with a regular car body is to calculate or research the drag coefficients and the force and power produced by the vacuum drag and produce a table that will list all of these values for the three aerodynamic profiles to perform an accurate comparison. Of course other variables such as the cross-sectional area of the body and the weight of the body will have to be standardized for the comparison of performance factors to be accurate.

 

[Aero_UoP]

the paper...
http://www.4g63.de/facts/vortexgenerator-evo-mitsu.pdf

On a side note, I've seen at least one production car with vortex generators very similar to ones used on airplanes; the Mitsubishi Lancer Evolution VIII. Whether they're helpful in terms of mileage, no idea.