The restrictor plate reduces the amount of air that can be sucked into the engine, the reduces horse power. This does two things:
1. It limits the cars top speed to around 190 mph (yes that is pretty fast for a stock car) but without it they would be over 210 MPH. NASCAR has decided that this is too fast for the drivers and not safe.
2. It limits the time a car can get up to speed.
The result of this is for most of the race all 43 cars drive around in one huge pack using the "draft" to pass. Exciting for most people, not my wife, to watch and no problem as long as everyone behaves. But if a tire blows or someone gets silly, and this usually happens, it can take out half the field due to the close proximity of each car.
The late Dale E. always said, we don't need no plate, if you don't like the speed, then get off the track. Ironic thing is, he died during the 2001 Daytona 500.
paul
