Porsche 911 Carrera 4
From Porsche press: The fabled wide-body, all-wheel-drive version Porsche 911 returns for the 2007 model year with several enhancements. These include tire-pressure monitoring systems, North American navigation systems that include maps of Mexico and Puerto Rico, and there’s a new exterior color -- Meteor Grey Metallic. Also available are 19-inch wheels in the new Turbo design. With its 325-horsepower 3.6-liter horizontally opposed six-cylinder engine, the 2007 Porsche 911 Carrera 4 is capable of accelerating from a standing start to 60 mph (96 km/h) in just 4.9 seconds and reaches 99 mph (160 km/h) in 11.2 seconds. Top speed on the test track for this car is 174 mph (280 km/h). When equipped with the optional Tiptronic S automatic transmission, the 911 Carrera 4 Coupe accelerates to 60 mph (160 km/h) in 5.3 seconds and reaches 99 mph (160 km/h) in 12.2 seconds. Top track speed is still an impressive 171 mph (275 km/h).
Porsche’s all-wheel-drive system uses a viscous multiple-plate clutch to send power to a central driveshaft that feeds a front differential to turn the front wheels with between 5 and 40 percent of the engine’s torque. This system of power distribution provides enhanced directional stability and balanced power and traction through turns and on slippery surfaces.
Such a viscous system exhibits outstanding cooling, even under high loads, and also is able to handle large changes in engine torque, for example, under all-out acceleration. The viscous coupling also reduces power loss due to friction between the clutch plates, adds only 110 lb. (50 kg) of weight to the vehicle, needs no maintenance and reduces potential drivetrain distortion under extreme braking.