News

NASCAR Sprint Cup Series

News Story

INSIGHT: RESTRICTOR-PLATE ENGINES

Unlike every other track that the NASCAR Sprint Cup Series runs on, Daytona International Speedway and Talladega Superspeedway are unique in that NASCAR requires teams to run special engine packages.

At these huge, high-speed tri-ovals, NASCAR mandates the use of something called a restrictor-plate. It’s not much to look at (see photo) – just a thin, machined aluminum spacer – but, as the name implies, it restricts the flow of the gasoline/air mixture from the carburetor into the intake manifold.

That cuts the horsepower of the 358-cubic-inch Sprint Cup engines from roughly 850 hp to about 450. NASCAR mandated the use of the plates after Bobby Allison’s horrifying airborne crash at Talladega in 1987, where his car tore a stretch of catchfence along the front straightaway at a time when qualifying speeds were in excess of 210 miles per hour.

The good thing about the plate engine is that it allows Cup drivers to race at safer speeds at Talladega and Daytona, typically in the low 190 mph range. But, racers being racers, they don’t simply bolt a restrictor-plate on a regular engine and go racing. No, that would be far too simple.

On a restrictor-plate motor, engine builders are constantly tinkering with every single aspect of the plate motors, trying to find even a couple of extra horsepower or a little better throttle response.

The drivers lament that plate motors don’t come to life fast enough: Let off the accelerator and there’s a noticeable break in momentum. So the engine departments at Toyota’s TRD, U.S.A., facilities and at Joe Gibbs Racing literally work year-round on making more powerful and more responsive restrictor-plate engines.

“The thing with unrestricted engines is you have all the throttle response in the world you want,” says Kyle Busch, driver of the No. 18 M&M’s Toyota out of the JGR stables. “Normally, we run those at all the racetracks where you have to get out of the gas anyway. At a place like Daytona or Talladega, where you can run wide open, because the engines are restricted, they seem to be numbed up. You get back to the gas and you're waiting. There's just a period of time where the motor is sitting there waiting for itself to catch back up.”

Now, mind you, Busch understands this is a necessary evil.

“If we ran unrestricted at Daytona, we'd have to get out of the gas,” he says. “We'd run 220-something miles an hour down the straightaway, but still have to get out of the throttle at the corner to not slide up the track, which might be fun for a while, but there's still the factor of getting cars airborne, so that wouldn't work.”

And that means the engine guys have to go to work, leaving no stone unturned in the search for better performance.

“With the restrictor-plate rules that we have now, it’s closer to an open engine than it ever has been,” says TRD’s Andy Graves. “But now that we’ve spent time with this package, everyone has started refining every small detail and it turns into a totally different engine package.”

In fact, TRD at one point had no less than 15 engineers committed solely to restrictor-plate engine research and development.

NASCAR veteran crew chief Philippe Lopez knows the implications. Lopez, who was the first employee hired by the late Dale Earnhardt and later by Hall of Fame Racing, is crew chief for Joe Nemechek’s No. 87 Toyota Camry, a car powered by TRD engines.

“They don’t ever stop working,” Lopez says of TRD’s engine department. “They are always working on restrictor-plate motors. As long as you’ve got four holes restricting the air, there are so many different combinations of head design, exhaust design and valves – just about everything on that engine – that you can just flog on it seven days a week, looking for one, two, three, four horsepower.”

A couple of extra horses might not sound much, but it can be critical when NASCAR mandates that all bodies must be identically configured. Long-gone are the days of one team having an aerodynamic advantage over another. Nowadays, it’s a horsepower hunt, which plays into the strengths of Toyota.

“We don’t ever come back to the track with less horsepower,” says Lopez. “If you come back with five or six (more horsepower), then it’s a good year. It’s incredible how small a gain that is, but five or six horsepower can be two tenths (of a second per lap).”

And it can be the difference between winning and losing, too, which is why TRD and JGR will be working harder than ever as the countdown continues to the 2010 Daytona 500.