IRL: Pike's Peak - Racing in Rare Air

RACING IN RARE AIR Advanced Electronics Help Oldsmobile Teams Achieve Peak Performance in Thin Air BY RICK VOEGELIN Fountain, Colo. - Just as human beings must become acclimated to the thin air at high altitude, the naturally aspirated...

RACING IN RARE AIR Advanced Electronics Help Oldsmobile Teams Achieve Peak Performance in Thin Air

BY RICK VOEGELIN

Fountain, Colo. - Just as human beings must become acclimated to the thin air at high altitude, the naturally aspirated racing engines that compete in the Pep Boys Indy Racing League have to compensate for the lack of oxygen at mile-high Pikes Peak International Raceway. In the "god old days," race car mechanics changed jets in mechanical fuel injection systems and adjusted spark timing with magneto ignitions. Now the adjustments required for high-altitude racing are performed electronically by the Delco Decise engine management system that regulates the fuel injection and ignition for Oldsmobile's undefeated IRL Aurora V8.

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 eighth round of the 11-race Pep Boys IRL series, the altitude is 5,317 feet above sea level and the barometer typically reads only 25.5 inches. 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.

"A naturally aspirated engine tends to lose power in direct proportion to the percentage reduction in barometric pressure," explains Ed Keating, lead development engineer for the IRL Aurora V8. "An engine needs oxygen to burn fuel, and the lower pressure at high altitude reduces the oxygen that is available for combustion. The result is that an IRL Aurora V8 typically produces 10 to 12 percent less horsepower at Pikes Peak than at sea level conditions.

"The Decise system has a sensor that measures the air pressure inside the air box that feeds the induction system," Keating reports. "The pressure inside the air box is produced by both atmospheric pressure and the ram effect generated by the air scoop at speed. The Decise system adjusts fuel delivery and spark timing according to that sensor reading, so the system is essentially self-compensating. In last year's race at PPIR, Oldsmobile teams were able to run their cars just as they would at any other track by allowing the Decise system to make adjustments for the higher altitude.

"The Decise system compensates for the lower air density by leaning the fuel mixture. Currently we are not making an altitude compensation for spark advance in the IRL Aurora V8. If an engine's spark advance is limited by detonation at sea level, then at high altitude you would be able to advance the spark timing and perhaps get the benefit of additional power. The IRL Aurora V8 is not detonation-limited at sea level, so we have not seen a need to alter the spark timing at high altitude."

The effects of thin air aren't limited to just engine performance. The lower air density also impacts the performance of cooling systems and aerodynamic devices - wings and ground effects - that are essential to peak performance.

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Series IndyCar