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Editorial

Is Your Plate Full?
The History of NASCAR Restrictor Plate Racing

 by Adam Sewell
February 12, 2001

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Some NASCAR fans claim that the four best races during the season are the events held at Daytona International Speedway and Talladega Superspeedway.  Daytona is the home of the Great American Race, the Daytona 500. Talladega is known as the world's fastest, largest, and most competitive track.  Daytona, which held the first Daytona 500 in 1959, is a 2.5 mile tri-oval and its turns are banked at 31 degrees. Talladega was patterned after the tri-oval shape of Daytona, but its length is 2.66 miles and its turns are banked at 33 degrees. Records have been set and broken at these two mammoth tracks. Bill Elliott came from nearly two laps down to win the Winston 500 at Talladega in 1985 without the aid of a caution flag. Elliott also set the qualifying records at both Daytona and Talladega in 1987 with speeds of 210.364mph and 212.809mph respectively.

The weekend of the Winston 500 from Talladega Superspeedway in 1987 changed the face of NASCAR racing. On Friday, Bill Elliott set the fastest recorded lap speed in a stock car, 212.809mph. When the starting grid was set on Saturday afternoon, it marked the first time that the entire field of cars for the race exceeded the 200mph mark. Once the race got underway on Sunday afternoon, one of the most frightening accidents in NASCAR history occurred.  Coming through the tri-oval on the front stretch, Bobby Allison blew a tire and his car started sliding sideways. As the car slid down the track, it went air born and slammed into the catch fencing just before the flag stand.  That entire section of the catch fence was ripped off and had it not been for the two steel cables that reinforced the fence, Allison's car would certainly have landed in the grandstands instead of bouncing back onto the track. The race was red flagged for several hours while NASCAR officials and construction crews rebuilt the catch fence. Once the race went back to green flag conditions, Bobby's son, Davey went on to win the race, his first career win. This one race probably changed the face of NASCAR more than any other. Bobby Allison's horrific crash led to the implementation of restrictor plates. Though NASCAR did not require restrictor plates until the start of the 1988 season, they did require a 390 CFM carburetor for the remaining two events at Daytona and Talladega in 1987. The smaller carburetor lowered speeds from the records set by Bill Elliott earlier in the season to Davey Allison's pole speed of 198.085mph at Daytona and Elliott's speed of 203.827mph at Talladega.


Diagram of a restrictor plate.
(click on image to enlarge)

A restrictor plate is a 3/16" thick piece of aluminum that is 5 by 5 inches with four holes punched in it. It is placed between the carburetor and the intake manifold. The restrictor plates rob the engines of about 40% of their horsepower by limiting the amount of air flow into the combustion chamber. They also make the engines run lower RPMs. The plates are put in place by NASCAR officials; at the beginning of the weekend, in the garage area. The restrictor plates are locked in a box and issued to teams strictly by the luck of the draw.  The restrictor plates are measured by the width of the holes punched in the plate. For example, the first plate used was a one inch restrictor plate.  This meant that the width of each of the four holes was one inch. The fastest pole speed achieved with the first restrictor plate was 196.996mph by Ken Schrader for the 1989 Daytona 500. NASCAR determined that Schrader's speed was too fast and they decided to shrink the restrictor plate down to 15/16 inches in time for the Spring race at Talladega in 1989. The fastest speed turned with the 15/16 inch plate was Bill Elliott's pole speed of 199.388mph at Talladega in May of 1990. This speed is also the fastest pole speed since the dawn of restrictor plate racing. NASCAR, again, made the restrictor plates smaller. For two races, the teams ran a 29/32 inch plate, and then for the May 1991 Talladega race, NASCAR issued a smaller 7/8 inch restrictor plate. The 7/8 inch plate stayed on the cars from May 1991 through the 1995 season. In 1992, NASCAR made a rules change that dictated the minimum spoiler angle. For the Daytona 500, the teams were required to run a minimum of 35 degrees, and for the 1992 July race at Daytona until October 2000, the teams were required to run a minimum of 45 degrees.  For the 1996 Daytona 500, NASCAR lowered the compression ratio to 14:1 and opened the restrictor plates back to 29/32 inches. In 1998, NASCAR lowered the compression ratio again to 12.5:1. With these rules, Joe Nemechek took the pole for the 1999 Winston 500 at Talladega with a speed of 198.331mph.  This speed became the second fastest pole speed since the introduction of restrictor plates.

NASCAR determined that the cars were getting too fast and decided to take a new approach to slowing the cars down. For the 2000 Daytona 500, NASCAR issued a 7/8 inch plate and also issued the front and rear shocks the teams were to use. The teams were also required to run a minimum spring rate of 345 pounds on the rear suspension. The spring rate is measured by the force it takes to compress a spring one inch. In other words, it would take 345 pounds of pressure to compress that particular spring one inch. Before the spring and shock rule, the teams had been using soft springs and stiff shocks to lower the rear end of the car to get the rear spoiler out of the air, resulting in less drag and higher speeds. The new shock rule resulted in a Daytona 500 that was pretty boring because the teams were not able to make their cars handle properly. So, in response to the complaints from the teams and fans, NASCAR did away with the requirement for the front shocks after the Daytona 500. In September of 2000, NASCAR made a very unexpected call. Because of the deaths of Adam Petty and Kenny Irwin, NASCAR issued restrictor plates at New Hampshire. This was the first time that NASCAR had ever issued them at a track other than Daytona and Talladega. Bobby Labonte took the pole at 127.632mph, but the big shock of the weekend came when Jeff Burton took the lead on the first lap and never gave it up, leading every lap on the way to victory. Many of the teams, fans, and members of the media criticized NASCAR for making the wrong decision.


A Winston Cup official monitors the installation of restrictor plates at New Hampshire last year.

The 2000 season definitely saw many changes to the face of restrictor plate racing. The most recent, and probably the best, was the aerodynamic package introduced for the final restrictor plate race of 2000 at Talladega. NASCAR's intentions were to cause greater drag, allowing them to open up the restrictor plates and give the cars more throttle response. All cars were required to run a 70 degree spoiler angle and have a lip across the top of the spoiler that faced forward. The Fords and Pontiacs had to widen their spoilers to 59 inches while the Chevrolets were allowed to keep their spoilers 57 inches wide. The front air dam was raised to 4 inches to allow more air to travel under the car. The most obvious change was the spoiler that was installed on the roof of all the cars. It was set 10 inches back from the windshield and was 1 3/8 inches tall by 40 inches wide. For qualifying, the teams were issued a 1 inch restrictor plate and Joe Nemechek took the pole at 190.279. The Saturday morning practice session was the first time that a large group of cars were able to draft with the new aero changes. The fastest practice speeds approached 198mph in the draft. NASCAR decided this was too fast and issued the teams a 15/16 inch plate for Happy Hour and the race. The race was absolutely incredible. There were 49 official lead changes, 21 different leaders, and Dale Earnhardt's come from behind victory was simply amazing.

Restrictor plate racing has been the source of some of NASCAR's most memorable and competitive races. It is also sometimes the source of frightening races.  "The Big One," a multi-car accident caused by the close packs of cars, is a direct result of plate racing and drafting. With the cars so equal at Talladega and Daytona, one slip by a driver can wipe out half the field.  Restrictor plate racing has undergone many rules changes since its induction in 1988. There have been eight changes in the size of the plate, two compression ratio changes and multiple aero changes to the cars. Also, the introduction of roof flaps has lowered the risk of the cars becoming air born. In the future, it may be possible that NASCAR would do away with the restrictor plates if the tracks and cars continue to become safer.

A special thanks to Jay of jayski.com for allowing me to use some of the information from his restrictor plate chart.

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