Apart from the PDK’s stated performance advantage — 4.5 seconds to 60 mph, or two-tenths of a second quicker than the six-speed manual for the standard 911 Carrera (and 4.3 seconds if you pop for the overblown Sports Chrono Package Plus) — we expect that in these economy-focused times, Porsche may choose to highlight how PDK pushes the latest 911 to deliver some fist-bump-worthy fuel efficiency.
A basic 911 Carrera currently is rated at 18 mpg city/24 mpg highway, or about 22 mpg combined. But for the new 911’s driveline, the combination of the newly direct-injected horizontally opposed six-cylinder engines and PDK make the new 911 some 13 or 14 percent more efficient than the current car, so a rear-drive 911 coupe might generate something approaching 25 mpg combined. Not too shabby.
Porsche’s conventional manual trumps the PDK ‘box in terms of transmission losses. However, the PDK’s seventh gear allows the engine to operate in a sweeter spot of its operating range which improves overall powertrain efficiency. Though it is a tall cruising gear, 7th gear in the PDK still provides enough mechanical advantage that the 911 can reach its top speed, while PDK’s 1st- through 6th-gear ratios are essentially identical to those of the six-speed manual.
Source: Inside Line