Seem to be illegal on NHRA pro cars at least?
"this was taken from a interview with John Force:
I come out of the roof hatch at Richmond and I got hung up on the bolts coming through the roof, so I told my guys, ‘Turn ’em over so I don’t hit ’em going out,’ so they were sticking up. We set the track record that weekend, but we were busted because they said they were vortex generators, that we deliberately turned them upside down to redirect the air, and I said, ‘No way. It was to keep from tearing my fire suit."
Heres a questioned sorta related answered by NHRA pro stock racer Warren Johnson:
With all of the fuss about aerodynamics, I have a question that may seem a little wacky. Most of the fish that have evolved in the sea over millions of years have a rough skin texture. Has anyone attempted to produce a rough-textured race car body? I'm told that golf balls have dimples in them for a reason.
Jim, you can go to the head of Professor Johnson's class. You've raised an excellent question.
Several years ago, 3M made a "fish scale" coating that was applied to the hulls of several boats competing for the America's Cup. I understand that this coating could indeed increase speed by reducing the friction between the hull and the water.
The rough texture of the "fish scales" worked like millions of miniature vortex generators. A vortex generator creates a boundary layer between the surface of the solid body and the fluid (or air) that is moving around it. You might think of the eddies that are formed by these vortex generators as tiny roller bearings that reduce the friction between the surface and the moving fluid.
Back in the glory days of the Trans Am road racing series in the late 1960s, Roger Penske put vinyl tops on his championship-winning Z/28 Camaros. There was speculation at the time that the rough texture of the vinyl was similar to the dimples on a golf ball. Several years later, it was revealed that the bodies had spent too much time in an acid-dipping tank, and the resulting damage to the roofs was concealed by the application of vinyl tops. Of course, those on the Penske team may have unknowingly improved their race cars' competitive advantage while covering up their indiscretion.
Though I've never seen fish scales or a vinyl top on a Pro Stocker, I have seen contingency decals carefully placed in aerodynamically sensitive areas. Now suppose that you trimmed the edges of the decals with pinking shears to create jagged edges like fish scales. No, that would never work — or would it?