Daytona 500, the 'Super Bowl of NASCAR' Requires Extensive Preparation by Chevy Teams to Optimize Restrictor-plate Engine Performance

DAYTONA BEACH, Fla. – Chevy teams in NASCAR's Nextel Cup Series put hundreds of man-hours into preparing for any one of the 36 races on the circuit. The Daytona 500, NASCAR's marquee event, probably gets the most attention out of all the races. While every team puts much emphasis on this premier race, additional preparation is needed as races here in Daytona Beach (and also at Talladega, Ala.) require the use of horsepower-slashing restrictor plates. Chevy's teams must tune their engines to get the most from them while fitted with these devices, which slow the speeds of race cars for safer racing at these tracks.

"Restrictor plates cut the horsepower of Chevy's – and our competitors' – engines from about 800 to about 400 horsepower," said Ondrej Tomek, NASCAR Nextel Cup engine engineer for Team Chevy. "This is necessary for safety reasons. Without the plates, cars would go much faster."

Without restrictor plates, race cars have the potential of reaching speeds of 230 miles an hour or more at the "superspeedway" tracks of Daytona and Talladega. In 2004, now-retired NASCAR driver Rusty Wallace reached speeds close to 230 mph testing an unrestricted car at Talladega and described the experience as "out of control."

"The makeup of these superspeedway tracks is such that the banking and the straights allow the cars to go much faster than at other tracks," said Tomek. "With restrictor plates, cars are limited to about 190 miles an hour here. That's about the fastest the cars can safely go and still have control. Faster than that and you exceed the limits of the tires and other parts."

Restrictor plates used in NASCAR's top level of racing are simple parts, merely metal sheets with four holes drilled in them. They are fitted between the engine's intake manifold and carburetor and limit the amount of air the engine takes in, thereby limiting engine speed to about 7000 revolutions per minute (unrestricted engines peak, or 'redline' at about 9500 rpm). The engines generate their peak horsepower above 7000 rpm; with restrictor plates the powerband is effectively limited due to the airflow limitation the plate imposes.

Teams must tune their engines to optimize the performance of the engines when fitted with restrictor plates. For example, a team may adjust the firing of spark plugs in an engine's ignition system but all teams keep their specific tuning methods a closely guarded secret. Factors such as air temperature, air density and vapor pressure all come into play when tuning an engine for restrictor-plate racing.

"Everybody has to run slightly on the conservative side here because the weather swings really fast in Daytona," said Danny Lawrence, assistant engine shop manager and trackside engine manager for Richard Childress Racing, which runs several Chevy teams in the Nextel Cup Series. "We have weather stations that clue us in to the changes we need to make and we also have a pretty good baseline from all of our records. Our computers tell us if we're close to where we should be and then we still have to fine-tune how the air gets into the engine and how the engine reacts to it. It's a balancing act; we try to get the best fuel mileage and get the most amount of power in the conditions that exist."

NASCAR regulates the size of the four holes in the plates, which currently have diameters of 7/8 of an inch. The sanctioning body reserves the right to change those specifications up until the start of the race, depending on track or weather conditions or if NASCAR simply feels horsepower is too high. As teams try to tune their engines to the amount of airflow that enters them, an unplanned change in hole size causes teams much trepidation.

"The cars and the engines get progressively better with testing and development," said Lawrence. "When NASCAR sees us reaching speeds of 190 mph we have a pretty good idea that they're going to cut us back. Even so, when they change the hole sizes – and each plate requires some different tuning – that sends everybody into a tailspin because we need to react to that change.

"We don't get much advance notice – they'll usually tell us right after qualifying. But every team gets the same changes so it's not like we're the only ones. We have enough experience to get through the race but after it's over we go back to the shop and do some more testing."