NASCAR has declined to penalize the 31 cars that failed inspection in the Sprint Cup and Nationwide Series at Daytona.
NASCAR confiscated the teams' roof flaps, which are designed to keep cars on the ground during spins and wrecks at high speeds, for further inspection.
Thirty-one cars, including 16 in the Sprint Cup Series, failed inspection before Thursday's practices at Daytona International Speedway.
NASCAR vice president of competition Robin Pemberton says the "functionality and safety aspects of the roof flaps were not compromised and the on track competition would not be impacted."
The roof-flap spacers had been illegally machined down to reduce weight.
NASCAR inspectors made those Cup teams install new, unaltered roof flaps before drivers were allowed on the track for the first of two practices.
Inspectors then went to the Nationwide garage and found similar issues on 15 cars.