IRL: Oldsmobile Pikes Peak Preview

FOUNTAIN, Colo. - The Oldsmobile teams preparing for the Pep Boys Indy Racing League Radisson 200 at mile-high Pikes Peak International Raceway on June 27 aren't changing jets and adjusting spark timing as they did in the years B.C. - "Before ...

FOUNTAIN, Colo. - The Oldsmobile teams preparing for the Pep Boys Indy Racing League Radisson 200 at mile-high Pikes Peak International Raceway on June 27 aren't changing jets and adjusting spark timing as they did in the years B.C. - "Before Computers." Now the adjustments required for high-altitude racing are performed electronically by the Delphi engine management system that regulates the fuel injection and ignition for Oldsmobile's undefeated IRL Aurora V8. "The race at Pikes Peak International Raceway presents three distinct challenges," said Joe Negri, GM Motorsports IRL/Road Racing Group manager. "First, we will be racing at high altitude, which affects the performance of both engines and chassis. Second, we will be running under a 10,000 rpm rev limit for the first time at this track, a reduction of 500 rpm since last year's race at PPIR. Finally, we will be returning to a one-mile oval after competing on three superspeedways." Just as mountain climbers must become acclimated to the thin air at high altitude, the naturally aspirated racing engines that compete in the Indy Racing League will have to compensate for the lack of oxygen at PPIR. At sea level, the earth's atmosphere produces a barometric pressure of approximately 30 inches of mercury. At the PPIR one-mile oval, the site of the fifth round of the 10-race series, the altitude is 5,357 feet above sea level and the barometer typically reads less than 25 inches of mercury. In this relatively thin air, just climbing a flight of stairs can leave a "flatlander" gasping for breath. A racing engine running at 10,000 rpm is subject to the same effect. "The mile-high elevation at PPIR typically reduces engine output by 10 to 12 percent from sea-level conditions," Negri noted. "Engine reliability is usually excellent at this event because the stress on critical components such as pistons is significantly reduced. A one-mile oval rewards an engine with strong torque and quick throttle response, and many Oldsmobile engine builders will be using special short-track engine specifications at this race." "A naturally aspirated engine tends to lose power in direct proportion to the percentage reduction in barometric pressure," explained Ed Keating, lead development engineer for the IRL Aurora V8. "An engine needs oxygen to burn fuel, and the lower air density at high altitude reduces the oxygen that is available for combustion. "The Delphi engine management system incorporates a sensor that measures the air pressure inside the air box that feeds the induction system," Keating continued. "The pressure inside the air box is produced by both atmospheric pressure and the ram effect generated by the air scoop at speed. The Delphi system adjusts fuel delivery and spark timing according to that sensor reading, so the system is essentially self-compensating. "Most Oldsmobile teams run their cars just as they would at any other track by allowing the engine management system to lean out the fuel mixture to adjust for the higher altitude." A normally aspirated IRL Aurora V8 gets a performance boost from the forward-facing air scoop behind the driver's head - a "natural" supercharger. At racing speeds on the fast PPIR oval, the scoop produces enough positive pressure to increase engine output by approximately 4 percent - about 25 horsepower. Unfortunately in racing, just as in life, there is no "free lunch." The price paid for this higher inlet air pressure is the increased aerodynamic drag produced by the air scoop. Thus the horsepower gains produced by the scoop's ram effect are offset by the higher drag. The effects of racing at high altitude extend beyond engine output. The lower air density also impacts cooling systems and aerodynamic devices such as wings, spoilers, and undertrays that are essential to an Indy car's performance. IRL engine builders will also have to contend with a new, lower rpm limit that is intended to rein in the rapidly escalating speeds on IRL tracks. Instead of the 10,500 rpm limit that was in effect at the two previous races at PPIR, the engines will be electronically limited to a maximum of 10,000 rpm. "Several builders developed interim revisions in engine tuning for the preceding race at Texas Motor Speedway, and they are continuing to refine their engines' power curves to suit the new operating range," said Negri. "We are also continuing our own testing program with the 4.0-liter engine to optimize its tuning for the 10,000 rpm limit. One of the competitive advantages of the Oldsmobile IRL Aurora V8 has been its high-rpm horsepower, so we now have to change our focus slightly to maximize power and torque at lower speeds." With the help of the IRL Aurora V8's sophisticated engine management system and the concerted efforts of ten independent engine builders, Oldsmobile is aiming to continue the longest active winning streak in a major American motorsports series with another victory in the rare air of the Rocky Mountains.

Be part of something big

Write a comment
Show comments
About this article
Series IndyCar