Aerodynamics is a complex subject and the results are dependent in many factors. The dimpled surface acts like a vortex generator and the size and location of the dimple. It is also affected by the shape and angle of incidence as referenced along the axis of the object.
In the 1990's when WJ was racing his Firebird Pro Stock, GM brought his car to the Georgia Institute of Technology and with the assistance of Boeing engineers, they spent considerable time working on the car to improve it. They ended changing the body panels and rake of the car. When Warren showed up at the Winternationals, the car went fast, got protested and ended hammering the quarter panels and putting duct tape.
If you want to see the aero effects, just tape wool strings to the body and take pictures and video. Done this in the past in airplane projects I had worked on and even Chrysler did so with the Mopar Missile in the early days of Pro Stock.
