According to a Porsche display, the German automaker timed three different 911s for comparison. The fastest was a 2009 911 Carrera S outfitted with Porsche’s new twin-clutch automated manual Porsche Doppelkupplung (PDK) transmission, PASM (Porsche Active Suspension Management) Sport, and “sports tires,” turning a 7:50 lap time.
Next was a 2009 Porsche 911 Carrera S (presumably with manual transmission) turning a 7:58. Four seconds slower was a current 911 Carrera S (presumably equipped comparably to the 2009 manual car), turning an 8:02.
Porsche says the PDK shifts 60 percent faster than the former Tiptronic S automatic, and offers a small improvement in fuel economy over the six-speed manual-equipped 911.
Source: Inside Line