One part of a NASCAR car engine that was implemented for safety reasons is now being pointed at as the cause for many of the multi-car accidents during races. Restrictor plates are used at NASCAR's super-speedways, including Daytona and Talladega, to slow cars down. The New Hampshire International Speedway was recently added to that short list of restrictor-plate tracks following the deaths of Adam Petty and Kenny Irwin on that track within months of each other.
A restrictor plate is a square aluminum plate that has four holes drilled into it. Hole size is determined by NASCAR and varies between 0.875 inches and 1 inch (2.2 to 2.5 cm). Restrictor plates are placed between the carburetor and the intake manifold to reduce the flow of air and fuel into the engine's combustion chamber, thus reducing horsepower and speed.
Restrictor plates were implemented in 1988 following Bobby Allison's crash into a retaining fence at 210 mph (338 kph), which endangered hundreds of fans. Also in 1987, Bill Elliott set the track record by running a lap around the track at 213 mph (343 kph). Some believe that if restrictor plates weren't used, NASCAR cars could race on super-speedways at speeds in excess of 225 mph (362 kph) due to the improved aerodynamics of the cars over the past decade.
While NASCAR officials contend that restrictor plates are needed to prevent high-speed crashes like Allison's, many drivers complain that restrictor plates are the cause of multi-car accidents. Restrictor plates reduce speed by about 10 mph, leaving the field of more than 40 cars bunched tightly as they race around the track at 190 mph. If one of these cars crashes, it usually causes several other cars to crash along with it.