The original concept of a NASCAR race car was that is was supposed to be composed of stock parts—parts you would buy in an auto parts store. In some respects that is true but not totally. The race car is a high performance racing machine designed to withstand high G-forces when banking on turns. Let’s look at what makes up this vehicle.

The first component most are interested in is the engine of a NASCAR racing vehicle. This engine actually is very close to that which you have in your car (provided you have a big engine) but it is customized so that it can withstand high temperature and torque. All parts in the engine of a are machined to within very tight specifications so that there is a minimum of friction. The carburetor is designed to let in the volume of air and fuel mixture required to sustain high speeds for lengthy spans of time. There are no fuel injectors in the race cars engine.

The first modification to the NASCAR vehicle was to smooth out the ride. Early races were run on tracks that were very bumpy and this causes a lot of damage. Today, the NASCAR vehicle is basically a body molded from sheet metal on a frame supported on the inside by bars made of sheet tubing. The vehicle is not a stock vehicle any longer as each component is hand-crafted and assembled. The car is built with safety in mind while giving it the ability to maintain speeds approaching 200 mph. Driver comfort is not the focus.

The NASCAR vehicle at one time was able to reach speeds in excess of 200 mph and that all changed in 1987 when Bobby Allison’s race car flew into a section of fence at the Talladega Speedway in Talledega, Alabama. Fans were injured in the stands and NASCAR took action to restrict the speed of the vehicle through what is known as a restrictor plate. This also gave birth to the term "restrictor-plate racing."

The physics of the restrictor plate have to do with reducing air intake into the intake manifold of the engine. Less air will result in lower combustion thus reducing horsepower. The restrictor plate is a sheet of metal with four holes bored in it at precise tolerances. The plate is then mounted between the intake manifold and the carburetor. After that, the NASCAR vehicle should not be able to exceed speeds of 200 mph.

It would seem like the restrictor plate would resolve the safety problem but many professional drivers have been asserting that it creates more potentially unsafe situations in a race. If you think about the difference between a motor scooter and a motorcycle you can see where a restrictor plate could create problems. Many times a motor scooter has an accident where a motorcycle could have avoided it because of its increased ability to accelerate (a motorcycle can accelerate quicker to avoid an oncoming threat). It is the same complaint among almost all of the racers with restrictor plates. They have identified situations where the cars bunch up and the driver only has one choice and that is to slow down. Speeding up to avoid the congestion is not an option because the other cars may be at the restrictor plate limit too.

But as for now, the restrictor plate is a requirement in the race car vehicle on the majority of tracks.