In Pixar's Cars, the season championship trophy is called the Piston Cup.
The Piston Cup is the central championship prize in the film's stock-car racing world. Lightning McQueen is competing for it at the start of the story, and the film's final race determines the season's outcome. The trophy's name is a playful reference to the piston, a fundamental engine component.
The opening race is the Dinoco 400, where Lightning, Chick Hicks, and The King finish together after a three-car crash. Because no driver is clearly established as the winner, a tiebreaking race is arranged in California. That event becomes the film's climactic competition.
The Dinoco 400 is the race, not the championship trophy. Dinoco is also the sponsor Lightning hopes to win, while Rust-eze is his existing sponsor. The Piston Cup therefore refers specifically to the season title and its trophy, not to a sponsor or an individual event.