How restrictor plates work

Pros and cons of restrictor plates will be debated thoroughly this weekend as the Nextel Cup series stops again at Talladega Superspeedway for the Aaron's 499.

In fact, a smooth track fresh from a fall repaving helped increase speeds so much that NASCAR made the four holes on restrictor plates 1/32 of an inch smaller for Friday's Busch series qualifying.

So what do these metal plates with four holes drilled into them do exactly once they are installed atop the carburetor?

The plates restrict air and fuel that flows through the carburetor and into the intake manifold on the way to the combustion chamber. This reduces horsepower and the speed of the cars.

Introduced in the name of safety in 1988 to lower speeds at NASCAR's superspeedways and cut down on the amount of debris that gets thrown into the grandstands, the restrictor plates caused drivers to race in large packs because it was harder for cars to find the extra power to pull away.

These large packs then run the risk of spectacular multicar wrecks if one driver loses control amid the close quarters of numerous drafting cars.