In Pixar's Cars (2006), Lightning McQueen races in the Piston Cup championship series.
The Piston Cup is the central competition in the first film. McQueen is a rookie contender whose ambition is to win the championship and secure the prestigious Dinoco sponsorship. A three-way tie at the end of the season leads to a final race in California, but McQueen's detour to Radiator Springs changes his priorities before that race is decided.
The series is a fictional counterpart to American stock-car racing. Its name echoes the piston-driven engines associated with traditional motorsport, while the racers, sponsors, pit crews, and oval-track events borrow familiar racing conventions.
The Dinoco 400 is a race within the Piston Cup season, not the name of the championship itself. Similarly, the World Grand Prix belongs to Cars 2, which shifts the franchise toward international racing. These related terms are easy to mix up because they all appear in the broader Cars racing world.