Restrictor plates are square-shaped pieces of aluminum with four one-inch holes. They are placed inside of a car's engine and regulate the amount of air and gasoline that the carburetor (which burns gasoline) and intake manifold (which distributes air) can use to create high pressures that allow for greater speeds.
Realizing that such accidents could be prevented if cars weren't able to reach speeds of over 210 miles per hour, NASCAR officially mandated that restrictor plates be used to decrease speeds at both Talladega Superspeedway and Daytona International Speedway. The committee chose to limit the usage of restrictor plates to these two tracks because Talladega and Daytona are much longer than most other NASCAR tracks (approximately 2.5 miles per lap) and contain a number of sharp turns that make extremely high speeds more dangerous.
Recently, the New Hampshire International Speedway was also added to the list of tracks that require cars to have restrictor plates attached to their engines due to two tragic accidents that occurred at one of the site's races.
The usage of restrictor plates is all about ensuring drivers' safety on race day. Technological improvements are constantly enhancing cars and allowing them to reach new heights in terms of their peak performance. Restrictor plates help counter the increased aerodynamics of modern race cars, preventing the cars from achieving a level of speed and horsepower that would be extremely dangerous for all drivers on the race track.
The holes are a crucial element to restrictor plates, as they allow just enough fluid to pass through and into the engine chamber, enabling race cars to perform at just below their maximum potential.
Restrictor plates were first introduced in 1987, following a crash at Talladega Superspeedway that saw driver Bobby Allison and his vehicle get launched into the fencing along the track.
The two race tracks that require the usage of restrictor plates (Talladega and Daytona) are widely considered to be among the most challenging tracks in all of NASCAR. Drivers cannot rely solely on speed during these races and instead must drive strategically and patiently at times in order to secure a victory.
All in all, restrictor plates have definitely changed the landscape of races at Talladega and Daytona. At the time of Allison's horrific crash in 1987, the top speed recorded by a car was 212 miles per hour. Since the implementation of restrictor plates, top speeds have dipped to a much safer threshold below 200 miles per hour, with the top speed of most recent Talladega winner Kevin Harvick sitting at 194 miles per hour.