Restrictors

Restrictors are devices installed in racing engines to limit power output by reducing the amount of air or fuel that can enter the engine.

These components are primarily used to equalize competition between teams, enhance safety by controlling top speeds, and reduce costs by limiting expensive engine development. Restrictors typically take the form of plates with precisely sized holes or tapered spacers placed in the engine's intake system.

NASCAR famously used restrictor plates at Daytona and Talladega until 2019, while various forms of restrictors are mandated in Formula 3, rallying, and endurance racing series like Le Mans. While restrictors create closer racing, they can sometimes lead to tightly packed fields that increase the risk of multi-car accidents.