Into Thin Air: The Search for Power at Mile-High Pikes Peak International Raceway FOUNTAIN, Colo., June 14, 2001 -- The barometric pressure at mile-high Pikes Peak International Raceway is low, but the pressure on GM Racing engineers is high....
Into Thin Air: The Search for Power at Mile-High Pikes Peak International Raceway
FOUNTAIN, Colo., June 14, 2001 -- The barometric pressure at mile-high Pikes Peak International Raceway is low, but the pressure on GM Racing engineers is high. The only blemish on Oldsmobile's 42-1 record in Indy Racing Northern Light Series competition is a lone loss last year at PPIR. This weekend Oldsmobile will return with a vengeance to the high-altitude oval for the Radisson Indy 200 with a potent short-track engine package that is tailored to the rarified air of the Rocky Mountains.
"The Infiniti program was certainly competitive last year at Pikes Peak, and it has become more competitive this year with the new engine," said Dick Amacher, GM Racing development engineer. "The record doesn't necessarily reflect the strength of their program. With the competition between manufacturers intensifying, GM Racing is continuing to improve the Oldsmobile IRL engine to maintain a competitive advantage.
"GM engineers have made significant changes to the IRL Aurora V8 engine since last year's race at Pikes Peak," Amacher reported. "In August we introduced high-velocity cylinder heads that improved midrange response and throttle response. At the start of the 2001 season, we released an updated induction system that boosts midrange torque and enhances fuel economy. We have refined our camshaft designs for additional horsepower and worked extensively on fuel mapping for the high altitude at Pikes Peak."
The naturally aspirated engines that compete in the IRL series depend on atmospheric pressure to fill their cylinders with fuel and air. At sea level, the earth's atmosphere produces a pressure of approximately 30 inches of mercury. Pikes Peak International Raceway stands 5,357 feet above sea level and the barometer seldom reaches 25 inches.
"Any naturally aspirated engine loses power in proportion to the reduction in atmospheric pressure," explained Amacher. "The lower air density at high altitude reduces the oxygen that is available for combustion and decreases power. Consequently an IRL Aurora V8 that can produce 650 horsepower at sea level produces ten to 12 percent less horsepower at Pikes Peak."
Oldsmobile teams can recover some of this "missing" power by carefully tuning the engine's electronic engine management system. "The Delphi system uses a sensor mounted in the air box to measure barometric pressure and oxygen sensors mounted in the exhaust pipes to monitor the air-fuel ratio," Amacher noted. "In production GM vehicles, these sensors provide feedback that the engine management system uses to reduce exhaust emissions and increase fuel economy. In a racing environment, engineers can use this data to fine-tune the fuel calibration for best power and maximum efficiency.
"A mechanical change such as increasing the compression ratio with special pistons can also improve engine performance at high altitude, but that requires compromises in other areas such as camshaft timing," Amacher continued. "The benefits of producing one-of-a-kind parts for a single race at Pikes Peak have to be weighed against the costs of design and development."
The IRL's return to Pikes Peak marks the start of the series' "short-track season" -- a 10-week stretch that includes a .75-mile oval in Richmond, Va., a 1.25-mile oval in Madison, Ill., and the 1.33-mile Nashville Superspeedway. These new venues will place a premium on quick acceleration and instant throttle response in traffic.
"GM Racing is evaluating new components that will reduce frictional losses and decrease the rotating inertia of the crankshaft assembly," Amacher revealed. "This approach can improve performance both at high altitude and at sea level. In conjunction with the revised cylinder head and induction system, these updates are intended to give GM racers quicker acceleration out of the corners and power on demand in traffic."
Oldsmobile engines have started on the pole in the last five IRL races at PPIR, just as they have started on the pole at all 43 IRL events since January 1997. Team Menard driver Greg Ray has monopolized the pole in the three previous races at Pikes Peak, setting the absolute track record at 179.874 mph last June. With another year of relentless development by GM Racing and the independent Oldsmobile engine builders, IRL racers will be flying low on the mile-high track.