As with most successful racers, Yunick was a master of the straddling the rules. Perhaps his most famous exploit was his #13 1966 Chevrolet Chevelle, driven by Curtis Turner. The car was so much faster than the competition during testing that they were certain that cheating was involved; some sort of aerodynamic enhancement was strongly suspected, but the car's profile seemed to be entirely stock, as the rules required. It was eventually discovered that Yunick had lowered and modified the roof and windows and raised the floor (to lower the body) of the production car. This car has many legends about it, and they were definitively debunked by the 2019 Dinner with Racers episode on Amazon Prime TV. Since then, NASCAR required each race car's roof, hood, and trunk to fit templates representing the production car's exact profile.