A restrictor plate is a metal plate with four holes that is installed between the carburetor (or, after 2011, the throttle body of the fuel injection system) and the intake manifold of a racing engine. By reducing the volume of the air-fuel mixture that can enter the engine, the plate cuts peak horsepower dramatically. At NASCAR's two designated superspeedways, the reduction has historically been used to keep race speeds below approximately 200 mph (320 km/h), a threshold regarded as a critical safety boundary.
NASCAR first used restrictor plates in a transitional context in the early 1970s during the shift from large-displacement seven-litre engines to the smaller engines that became standard. This period was not what is commonly meant by "restrictor plate racing" because not every car was subject to the restriction.
The modern era of restrictor plate racing was triggered by a crash involving Bobby Allison at the 1987 Winston 500 at Talladega Superspeedway. Allison's car blew a tire at approximately 200 mph (320 km/h) near the tri-oval, became airborne, and tore through nearly 100 feet of catch fencing, injuring several spectators. NASCAR experimented with smaller carburetors at subsequent superspeedway races that year, found them insufficient to adequately slow the cars, and mandated restrictor plates at Daytona and Talladega beginning in 1988. When the Busch Grand National series began racing at Talladega in 1992, the plates were implemented there as well.
A third application came in 2000, when two fatal crashes involving stuck throttles at New Hampshire International Speedway led to a one-time use of restrictor plates at that oval for the 2000 Dura Lube 300. The measure was not repeated there.
The defining characteristic of restrictor plate races is the formation of large, closely bunched groups of cars — known as "the pack" or "the draft." When horsepower is restricted and drag coefficients across the field are similar, cars cannot generate enough power to pull away from the group. Instead, they draft in tight formations, trading slipstream advantages in search of speed. At Daytona and Talladega, the width of the tracks — particularly Talladega, which is wide enough for three or four columns of cars running side by side — amplified these effects.
A frequent consequence of pack racing is the multi-car crash commonly called "the Big One." When a car loses control at high speed in the middle of a tightly packed group, adjacent cars have little time or space to avoid contact. Talladega Superspeedway has historically been the more frequent venue for large pileups. The 2011 Daytona 500 was notable for an unusually high number of caution periods, including an early 17-car incident.
The number of official lead changes in restrictor plate races has historically been very high. At Talladega, races have exceeded 40 official lead changes sixteen times since 1988. The 2010 Aaron's 499 produced 88 official lead changes across the race and its green-white-checkered attempts.
The first race run under the new restrictor plate rules was the 1988 Daytona 500, where the lead changed 25 times officially and featured extended side-by-side racing in the final 50 laps among Bobby Allison, Darrell Waltrip, Neil Bonnett, and Buddy Baker. In the years that followed, teams progressively mastered the aerodynamic nuances of the format, refining drafting techniques and increasing the size and speed of the packs compared to the early plate races of 1988 through 1990.
In 2011, NASCAR completed its final full season with carbureted engines and announced a switch to electronic fuel injection for 2012. The new EFI system was compatible with restrictor plates, allowing their continued use. The last race run under the original plate configuration was the 2019 Daytona 500. Beginning with the 2019 race weekend, NASCAR replaced the fixed-hole restrictor plate with a variable-sized tapered spacer — a device that funnels air more smoothly into the manifold while still limiting the volume of airflow. At the same time, larger rear spoilers, larger front splitters, and aero ducts were mandated to add drag and partially offset the power increase from the spacer. While the change improved passing and racing quality, speeds climbed perceptibly past 200 mph and in some cases reached 205 mph (330 km/h).
In 2022, NASCAR extended restrictor-style rules to Atlanta Motor Speedway after a repaving and reconfiguration raised speeds to concerning levels at that circuit.
Outside NASCAR, restrictor plates and air restrictors serve related functions in other forms of motorsport. Formula SAE uses a 20mm restrictor to limit competing cars to manageable power levels. World Rally Championship regulations have mandated restrictors for turbocharged engines since the 1990s, following the banning of Group B cars whose unchecked power made them too dangerous. The FIA GT Championship, Le Mans Prototype classes, and the Deutsche Tourenwagen Masters have all used air restrictors as a competition-balancing mechanism. In 1995, Toyota Team Europe was found to have used an illegal device to bypass the WRC restrictor, gaining an estimated 50 horsepower; the team was stripped of its season results and banned for the following year.
Restrictor plate racing has always generated debate. Critics argue that the large packs reduce the role of individual driver skill — that raw speed advantage is neutralized and position changes too often come through accident rather than ability. Supporters counter that the format demands its own tactical intelligence: drafting partners must be chosen, timing of moves must be precise, and the moment to break from the pack requires judgment. Rusty Wallace tested a Cup car at Talladega without a restrictor plate in 2004, reaching 240 mph (390 km/h) on the backstretch and a one-lap average of 221 mph (356 km/h), later stating it would be "insane" to race in a pack at those speeds. Darrell Waltrip, ahead of the first plate race in 1988, noted that the restriction actually gave drivers more tools — forcing them to "think their way" past opponents rather than simply overpowering them.