History: Porsche Double-Clutch Genealogy
by Marc Noordeloos
America had its first taste of a dual-clutch transmission in the 2004 Audi TT 3.2, but the innovative technology traces its roots back much further. French engineer Adolphe Kegresse developed the concept in the late 1930s but was unsuccessful in getting it to production. Porsche experimented with a dual-clutch gearbox in the 1960s, shelved it due to persistent problems with rough shifting, and then resurrected it in the 1970s for a German government project. Real progress had to wait until Porsche took it to the racetrack in the 1980s, although the company always hoped that the technology would trickle down to production cars.
The company's racing engineers figured that no-lift shifts could help reduce turbo lag, and so they tested the gearbox, called PDK, in a retired Group C 956 in 1983. The setup was similar to a modern dual-clutch transmission, but there was a manual clutch pedal for pulling away from a stop. Early problems included oil leaks and clutch issues. A PDK was first used in public during practice at a Group C race at Kyalami in South Africa, but it was decided that the gearbox wasn't ready for prime time, and it wasn't used for the race.
Testing continued in 1984. The goal was to improve reliability and shift speed and to reduce the weight of the gearbox, which at the time added some ninety pounds to the back of the car. The system was used for the first time in a race that year at Imola, but it lasted only two laps before suffering hydraulic issues.
By 1985, Porsche regularly campaigned a car with PDK as its third entry in Group C races. Wins were elusive, but durability improved.
Porsche frequently raced cars with PDK in 1986, except during the 24 Hours of Le Mans due to dependability concerns. At that point, the transmission carried about a one percent advantage in lap times despite its weight penalty. The automaker finally got what it wanted - a PDK win - at Monza, helped by the fact that the race was only 365 kilometers (227 miles) instead of the usual 1000 kilometers (621 miles). Development of the gearbox continued, and the weight disadvantage eventually was reduced to less than fifty pounds. Reliability still affected results, however.
PDK was no longer a priority for Porsche after it withdrew from Group C in 1987. The far less sophisticated Tiptronic automatic debuted in the 1990 911 Carrera 2. Now, twenty-five years after Porsche got serious about dual-clutch technology, customers finally can enjoy what the company always hoped for - a PDK transmission in a road car.