The rear scoops are functional as they direct cold air to cool the brakes. There are two kits out there for the C5. One you actually have to cut the rocker panel and bolt the scoop on the car with the functional tunnel to cool the rear brakes. The other is purely rice with double sided tape on it. So...
Scoop w/ complete kit and cutting holes = functional mod
Only the outside piece w/ tape = Rice C5
I decided against doing it on mine as the rear brake is not as important as the fronts. If I see fade, it will come from the fronts first.
Good race, it is believable as C5 drivers are really bad drivers. Myself included