Restrictor plates are devices installed between the carburetor and intake manifold that restrict the amount of air and fuel entering the engine's combustion chamber. NASCAR Sprint Cup currently uses restrictor plates at Daytona International Speedway and Talladega Superspeedway.
the device limits the power output of the motor and hence slows both the acceleration and the overall top speeds obtainable on the tracks where the cars are so equipped. These restrictions are supposedly in the interest of driver and fan safety, although many members of both of these groups feel that the close packing of cars and their inability to achieve separation may actually make the racing at these tracks more dangerous, as there are often massive and frightening multi-car pileups during races (especially at Talladega). Such crashes are dubbed "the big one" by drivers and fans and usually happen once per race. On rare occasions there are multiple such incidents, or on even rarer occasions, none. It certainly makes for a different style of racing at these events than that which occurs at the other superspeedways used by NASCAR, as reduced power makes it more difficult to pass other drivers.
Drivers often form long chains, which, due to the lack of air resistance, typically travel faster than single cars. This type of racing is often referred to by fans, drivers, and crew members alike as restrictor plate racing.
Reason for restrictor plates
There have been three reasons that NASCAR used restrictor plates in its history.
The first use came in 1971 as part of NASCAR's plans to reduce the size of engines from 427 cubic inches (7.0 L) to 358 cubic inches (5.9 L). In order to allow teams with smaller budgets to race the larger engines, NASCAR made mandatory the use of a restrictor plate to be placed on larger engines to equalize performance with smaller engines. The transition ended in 1974, when NASCAR banned the larger engines, and went to the current 358 cubic inch (5.9 L) formula. This was a transitional process and, as not every car used restrictor plates, this is not what most fans call "restrictor plate racing."
The second use came following the terrifying crash of Bobby Allison at the 1987 Winston 500 at Talladega Superspeedway. Allison's Buick LeSabre flew tail-first into catchfencing early in the event, injuring spectators. After a summer where the two subsequent superspeedway races were run with aids to prevent cars from flying, and smaller carburetors (390 cubic feet per minute instead of 750 cubic feet per minute), NASCAR imposed restrictor plates again, this time at the two fastest circuits, both superspeedways: Daytona for all NASCAR-sanctioned races and Talladega for Cup races. The Automobile Racing Club of America also enforced restrictor plates at their events at the two tracks. In 1992, when the Busch Series began racing at Talladega, the plates were implemented.
However, restrictor plates are not used for Craftsman Truck Series trucks; rather, air intake, aerodynamic, and spacer restrictions were implemented for those races, combined with the aerodynamic disadvantage of the trucks, allows NASCAR to eliminate the use of such equipment for the trucks.
The third use came in 2000. Following fatal crashes at the New Hampshire International Speedway during the May Nationwide Series and July Cup Series races, NASCAR imposed restrictor plates for Cup cars to slow the cars headed towards the tight turns as part of a series of reforms to alleviate stuck throttle problems which were alleged to have caused both fatal crashes. The plates, used for the Whelen Modified Tour events at the track, were used just once at the 2000 New Hampshire 300 event, allowing Jeff Burton to dominate by leading all 300 laps in the ensuing race. Due to the lack of passing (and by most all fan's accounts, an extremely boring race at a track that already produced boring racing) and the addition of an automatic kill switch in the case of a stuck throttle, the use of restrictor plates was discontinued at New Hampshire for the following race for Cup only. (Restrictor plates are still used for the Whelen Modified Tour.)