Porsche has been developing the PDK semi-automatic transmission in competitions for four years, and the programme ended when Hans-Joachim Stuck won this year’s German Würth Supercup series in his lightweight 962C PDK.
The day after the final round, at the Nürburgring, we were invited to drive the 650 bhp Group C car and gather impressions of the twin-clutch transmission, which now goes into the intensive development stage for passenger cars of the 1990s. It will be expensive without doubt, but offers the advantages of automatic transmission fully controlled by the driver, dispensing with the power-absorbing hydraulic torque converter.
The cockpit of a 962C is a snug fit, and the matt black fascia is riddled with strange gauges which include water temperatures on both banks of the twin-turbo flat-six, fuel pressure, oil pressure, oil temperature, fuel consumption, the tachometer with a yellow line at 8200 rpm, and an array of red, white and orange lamps.
There was, to be truthful, no chance to check the gauges properly even once in eight laps, since the 962C demands total attention around the neue Nürburgring, but the engineers had sufficient faith to tell me to stop only if any of the lights came on.
The gear lever is short and sturdy but does not have a gate. Moved to the right it selects neutral by disengaging both clutches, and to select first gear it is pulled to the left and back, with a very light touch since it is actually an electrical switch.
Upward shifts are effected by pushing the lever forward, downward shifts by pulling it back, and to make the driver’s life easier still there are two thumb-buttons on the steering wheel which replicate the lever movements, the upper button for higher gears, the lower button for lower gears. It all sounds terribly easy, and became so once the alien experiences of driving a powerful racing car on an unfamiliar racing circuit had been absorbed.
PDK is shorthand for Porsche Doppelkupplungsgetriebe and the transmission consists of two shafts, each of which has its own clutch. One shaft carries first, third and fifth gears, the other second, fourth and sixth gears (the 962C does not have sixth though), and the shafts are alternated by opening one clutch and clamping the other, instantly.
The principle is not complicated in engineering terms but control is a very different matter— a nightmare of solenoids, switches and dual hydraulics. Hans Stuck lost the 1986 World Sportscar Championship for Drivers because a twopenny electrical contact failed at the Norisring, something which took five minutes to trace and five seconds to rectify, but that was Derek Bell’s gain.
A digital display directly in front of the driver shows two numbers, the gear selected and the gear engaged, so from the pits the numbers read 1/1 when first was engaged. Since the shifting is immediate, the numbers match throughout acceleration (2/2, 3/3 and so on), but downshifting is child’s play since the lower gear cannot be selected until road speed has fallen appropriately.
At full speed on the straight in fifth gear, the driver would knock the lever backwards three times, or punch the lower button three times, to select second gear for the corner ahead. The readout will show 5/4, 5/3 and 5i2 in quick succession, and the lower gears will be engaged in sequence in the braking zone, leaving the transmission ready for acceleration when the corner is reached.
The clutch has a long, heavy travel and bites suddenly near the top of the movement, which is rather disconcerting. It is only needed for starting off though, and, having managed to get the Porsche moving without stalling, pressure on the organ-stop throttle literally launched the car down the pit lane.
Lever forward for second and the Concorde-like surge continues, onto the clear track and towards the Castrol ess-bend. The engine note has dropped, and a dab on the brakes sets the car up for the chicane before accelerating downhill to the second-gear Veedol curve.
Each upshift is instantaneous, and offers Stuck and Bell the advantage of keeping the turbocharger spinning freely, eliminating the so-called turbo lag. Downhill through the Ford curve, taking fifth for a couple of seconds, then pull the lever three times while braking for the horseshoe-shaped Dunlop curve. This is good!
The first couple of laps were exploratory, and nearly included an unintended visit to the pit-lane at the Romer curve. Doing what comes naturally, I was using the gear lever conventionally, pulling to change down one ratio at a time, but as the car and the track came into focus I began to realise its advantages and pre-selected for the corners ahead.
Not until my third lap did I remember the thumb buttons, which immediately became favoured. Engineer Walter Naher had warned with a smile, and with his arms crossed: “Don’t forget, if you’re in the corner the controls may be reversed!”. It sounded like “Sound Barrier” all over again; that mythical shaking of the controls as the speed of sound is reached, but really could not have been easier.
It is impossible to damage the engine since it cannot downshift prematurely, a point Stuck makes strongly. “It would be a big step forward now for Formula One, especially with the normally-aspirated cars which don’t have a weight problem. It’s so much easier for the driver, you can’t break the engine with bad shifting, and the more corners there are, the greater is the advantage. It would be fantastic for the street circuits.”
All very true. I found, as a journalist, that PDK was giving me the opportunity to concentrate on the car, its behaviour, and on the lines of the circuit without distractions. For Stuck and Bell, the advantages have been the stepless, fractionally faster acceleration, elimination of turbo lag, the chance of being in the correct gear at all times, and more. . .
“You can change gear in the middle of a corner,” says Stuck, “and I like it especially when it’s raining. If the tail begins to slide, you simply press the button and change up a gear, and the car accelerates better.”
It was possible recheck this on the uphill run from the Dunlop curve, which is second-gear for Stuck and the novice alike. It’s the one place, perhaps, where the inexperienced driver need not lose too much time, and with familiarity I could, indeed, bump the outside kerb and feel the rear wheels losing grip under the strain of transmitting full power. Press the top button, third gear responds, and the 962 is launching itself up the gradient towards Yokohama curve, where heavy braking is needed for the 90° left.
All that power in a thoroughbred racing car weighing 850kg becomes very addictive. The brakes are superb, naturally, and at 20 seconds off Stuck’s best times the ground effects are hardly working, allowing the Porsche to offer a reasonable ride. There is springing, it can be felt over the bumps, and although the engine is loud it is not ear-splitting.
The overriding impression, especially out of slower corners, is of colossal acceleration and of the speed with which the needle reaches 8200 rpm. Logically, though, fifth-gear acceleration on the straights is impressive but not searing, and you can begin to realise why drivers always want even more power!
The 962C PDK would unquestionably make the world’s finest road-going supercar, if only it could be legalised, and eight laps of the Nürburgring passed quickly, in 14 minutes to be exact.
The signal to come in was shown all too soon as I was ready to drive another eight laps, to take a higher gear here and there, to find a better line for the Bit-curve, to do this and that to narrow the embarrassing 20-second disparity! I remembered driving the six-speed 959 road car at the Nürburgring last August — the transmission then made my right arm ache after 20 minutes and left me not unwilling to stop for a think!
Porsche’s next Group C car will be powered by the latest Indy V8 engine which, with a lower crankshaft line, will require a completely new gearbox. It will have a conventional transmission, competitions director Peter Falk tells us, and development of the PDK system will now be progressed for the passenger car lines: 944, 911 and 928. There are already prototypes of all three at Weissach, some without a clutch pedal at all, and within five years PDK will be offered as an expensive option.
There have been many automatic, or semi-automatic transmission designs in racing throughout this century and WB could doubtless reel off a long list. Eminent designs have included the Wilson pre-selector on the ERA, HWM and Connaught Grand Prix cars, the Cotal electric gearbox used by Delahaye, the Hobbs Mechamatic raced by David Hobbs in Jaguars and Lotuses a quarter of a century ago (sorry David!), the GM two- or three-speed designs used in Jim Hall’s Chaparrals, and if you like, Porsche’s Sportomatic transmission with electric particle clutch-plate separation.
Is PDK worth getting excited about, or is it just a new approach to an old idea? It is heavier than a conventional transmission, certainly, though the penalty has now been reduced to just 15kg and Porsche can live with that because it gives a net improvement in lap times.
It was designed at Weissach around 1970 but shelved for at least ten years because it needed the new electronic technology to perfect all its advantages; for the future it will offer Porsche’s customers the benefits of higher performance, better economy, six forward speeds perhaps, and a better chance of being in the correct gear at the right time.
PDK can also be tailored to allow fully automatic gearchanging, up and down the box, with override control at the driver’s hand, and these refinements have already been tested in the 962C though not actually in a race.
At the very least it will be a fascinating device for Porsche’s future customers to play with, and one I would love to try in a 944 Turbo for instance, but only time will tell if it is a major breakthrough in automatic transmissions.
We should know by the year 2000! MLC