Restrictor Plate

The restrictor plate is a thin, square aluminum piece with four holes that restricts airflow from the carburetor to the engine, resulting in less horsepower and a reduction in the stock car’s speed. It is located between the engine’s carburetor and intake manifold.

The restrictor plates, 1/8 of an inch in thickness, range in hole size from 3/4 of an inch to 1-1/2 inches. As the hole sizes decrease, it will have more of an effect on the reduction of horsepower.

From 3/4 of an inch to 1 inch, the plates increase in size by increments of 1/64 of an inch. From 1 to 1-1/2 inches the plates increase by increments of 1/16 of an inch. The restrictor plate size being used for the 2008 season is 57/64 of an inch.

 

 

The restrictor plate is used at the NASCAR Sprint Cup Series’ two largest superspeedways, the 2.5-mile Daytona International Speedway and the 2.66-mile Talladega Superspeedway. NASCAR distributes the restrictor plates to the teams during those race weekends, collects them following on-track activity each day as well as at the conclusion of the event.

The version of the restrictor plates currently in use was introduced to the NASCAR Sprint Cup Series in 1989, beginning with the season-opening Daytona 500 at Daytona International Speedway.