Ed "Ace" McCulloch, a champion ex-racer and a crew chief at Don Prudhomme Racing, one of the top team owners, is explaining how he programs his multistage five-disc clutches. Each disc is on a pneumatic timer, and progressive engagement is controlled to fractions of a second. In the old days, a driver dropped the clutch at the start and up-shifted through gears. Today, there are no gear changes in Top Fuel and Funny Cars. Instead, the preprogrammed clutch packs mediate engine power to the wheels with no control from the driver. His job-or hers, for several women are among the drag-racing elite, including Shirley Muldowney, who raced at the age of 62 in Englishtown, New Jersey, this summer-is to "get a good light," that is, get a quick reaction time when the light turns green on the tree.
"At the light," McCulloch says, "the engine is turning 8,000 rpm, but the axle ratio is only 2,000 rpm-a slippage of 6,000 rpm. By operating a series of levers-there can be up to 12, but we don't use that many-the clutch pressure and axle ratio rises incrementally. It doesn't reach 1:1 until 3 seconds into the run."
The race, then, is more than half over before the wheels are dealing with the engine's full power. For 3 seconds, the clutches are being broiled by more than 6,000 horsepower. A half-hour later, they still smoke like ribs on a spit. No surprise that three of the five discs in each clutch must be replaced after every run. The remarkable thing is that a successful team can produce race results within a hair of a previous run-in fact must do so for an official record time to stand in the books, because any record must be backed up at the same event by another run that clocks within 1 percent of the speed.
Engine power is fully preprogrammed as well and matched to the clutch-engagement curve. McCulloch first assesses whether the track is slippery or "tight," advancing or retarding the car's cylinder timing and trimming fuel flow to suit. "I can program 12 timing changes in a run," McCulloch says. "At the start, I use about a 20-degree retard, which knocks the rpm down to 7,700-that 'relaxes' the tires, so you don't get tire shake." Then McCulloch advances the ignition for more power, until the next clutch engagement, when he retards the speed again to keep from breaking the tires loose. The amount of clutch and retard depends on how slippery the track is as well as on weather conditions like air pressure and humidity. "It's all," McCulloch says, speaking about the car, "adjustable."
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