Porsche Shifts Swiftly to PDK
Half of Porsche car buyers opting for impressive new dual-clutch transmission.
BY TOM MURPHY Ward's AutoWorld, Oct 1, 2009 12:00 PM

TO SOME PERFORMANCE PURISTS, A Porsche with an automatic transmission borders on heresy.

But many U.S. buyers of Stuttgart's legendary sports cars apparently have gotten over it and are happy to drive Porsche AG's new dual-clutch transmission, known as Porsche Doppelkupplungsgetriebe (PDK).

Launched last October in the U.S. in the '09 911 and a few months later in the Boxster roadster and Cayman coupe, the PDK transmission has doubled the take rate for automatics in those three vehicles.

Roughly half of the 5,800 Porsche sports cars sold this model year in the U.S. have been equipped with the PDK. The take rate for the previous Tiptronic automatic was about 25%, the auto maker says.

The old automatic wasn't bad, and Porsche collected plenty of royalty checks from other manufacturers willing to copy it. But it required a torque converter and, overall, weighed 22 lbs. (10 kg) more than the new PDK.

Dual-clutch transmissions have become the rage in performance applications since they appeared first in the Volkswagen Golf R32 and Audi TT, developed with drivetrain specialist BorgWarner Inc. The TT was the first vehicle to reach the U.S. with the DCT, in summer 2003.

Porsche claims the world's first application of a PDK in the 956 in 1983, but it wasn't until BorgWarner and Volkswagen AG paired up many years later that the technology was ready for high volume. Plants dedicated to manual transmissions now could be retooled easily for DCTs.

Since then, the technology has filtered out to a wide range of applications, including the New Beetle, BMW M3 and Z4 roadster, Nissan GT-R and Mitsubishi Lancer Evolution.

Next year, Ford Motor Co. will introduce a “PowerShift” DCT, engineered in tandem with Getrag GmbH & Cie KG, on the all-new Ford Fiesta and Focus small cars in the U.S.

A DCT connects two separate gear sets, with even-numbered gears on one shaft and odd-numbered gears on another, to the engine by two parallel clutches. When one gear is engaged, the next gear, thanks to the second clutch, is pre-selected, ready for swift engagement.

The technology allows automatic shifting of gears that is extremely fast, yet significantly smoother and more precise than single-clutch automated-manual transmissions, which now are passé. The driver can shift manually, if desired.

The PDK largely mimics that of other DCTs, but Porsche deploys two separate sumps using two different fluids ? one optimized for the gears, the other for the wet clutches.

Most DCTs use wet clutches, but BorgWarner will supply the hydraulic actuation module for Fiat SpA's first dry-clutch DCT, launching later this year.

ZF Friedrichshafen AG developed the PDK with Porsche and assembles the units in Brandenburg, Germany.

Porsche says its PDK is better than the old Tiptronic in every way, particularly in the area of fuel economy.

At 62 mph (100 km/h), the 7-speed PDK lets the engine run 30% slower than the 5-speed Tiptronic. On the highway, the Boxster S gets 29 mpg (8.1 L/100 km) with the PDK vs. 26 mpg (9 L/100 km) with the Tiptronic.

And performance is better, too, with faster lap times and better stability when downshifting and braking as power flows uninterrupted to the wheels.

The Carrera 4S with PDK sprints to 60 mph (97 km/h) in 4.3 seconds vs. 4.5 seconds with the 3-pedal manual. For an extra $960, the Carrera 4S can be had with a Sport Chrono Package that sharpens throttle response and holds gears longer, enabling a 4.1-second dash.

After spending two weeks with the PDK in the Carrera 4S and Boxster S, Ward's editors find the new transmission to be dynamic, intuitive and thrilling.

Shifting is smooth, succinct and amazingly fast, like a rapid-fire Beretta.

In automatic mode, most drivers quickly recognize the PDK always shifts faster than the old Tiptronic, and certainly faster than a manual. Porsche says the old Tiptronic requires 0.3 seconds to react to a driver's input and 0.75 seconds to change gears. The PDK reacts in a lightning-fast 0.04 seconds and changes gears within a half-second.

Upshifts in automatic mode come whenever the transmission controller decides the engine speed is well suited for the next gear, boosting fuel economy while sacrificing no performance. The heavier the throttle input, the longer each gear is held.

In manual mode, the PDK allows ample runs to the red line, and gear selection can be performed with the console-mounted shifter or with paddles mounted to the steering wheel.

Positioned conveniently at 9 and 3, the forward gears are engaged by pressing either paddle with the base of the thumb. For downshifts, paddles on the backside of the steering wheel are controlled by pulling back with the fingers.

With such a magical exhaust note, manually downshifting with the PDK is like conducting a Bavarian symphonic masterpiece. On the highway, cruising at speed in seventh gear, a bootful of throttle will force the PDK into fourth or even third gear, without being lurchy or thrashy. At slightly slower speeds, a smooth 6-2 gear shift is not uncommon.

Our one complaint comes before the PDK has done much of anything. At a standstill, even under a heavy accelerator pedal, the transmission seems balky and hesitant, similar to the annoying lag common with some older turbocharged engines. A car with 385 hp is supposed to launch with more neck-snapping drama.

Porsche says in standard mode in casual driving, the PDK is designed to mimic the slight lag experienced with the Tiptronic torque-converter transmission, for maximum efficiency.

Many drivers will barely notice the lag. The Sport Chrono Package is worth the money if the hesitation is bothersome.

With either package, the PDK manages 18/26 mpg (13-9 L/100 km), while the manual Carrera 4S gets 18/25 mpg (13-9.4 L/100 km).

Porsche's next application will be the new Panamera sedan, which arrives this year in the U.S. only with the PDK.

The Cayenne CUV is not expected to receive the PDK because the torque converter in the Tiptronic transmission is necessary to accommodate towing.

The DCT is here to stay. Earlier this year, participants at the Car Training Institute Symposium in Berlin predicted the DCT will be the leading transmission by 2020.

BorgWarner expects global production of DCTs to grow an average 42% annually to 5 million units in 2014.

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