This summer, Porsche is introducing the next generation of the 911, the latest version of the unique rear-engined concept that's been continually developed over its 45-year evolution in order that it remains relevant in changing times.
By introducing a range of new technologies, Porsche has built on the outstanding reputation of the 911 to further optimize the car for today's driving environment. All-new 3.6 and 3.8 liter flat-six engines will feature Direct Fuel Injection (DFI), and the option of the Porsche Doppelkupplungsgetriebe (PDK) double-clutch transmission, are highlights marking a quantum leap in the car's development.
The four new 911 models - two Coups and two Cabriolets - offer increased performance and efficiency. With either a six-speed manual gearbox or the PDK transmission, the Carrera Coup offers outstanding fuel economy of 29.4mpg combined. Furthermore, CO2 emissions of the 3.6-litre engine are down by up to 15%. And these engines, 13 lb lighter than before, also outperform European emissions regulations.
Standard on the Cayenne V-engines since 2007, Porsche is now moving over to Direct Fuel Injection (DFI) for the flat-six engines in the 911 series. Forming exactly the right mixture of fuel and air directly in the combustion chamber, this sophisticated technology serves to develop more horsepower and torque from less fuel.
As well as offering lower running costs, the direct fuel injection engines fitted in the 911 are also more powerful than the previous generation units. Maximum output of the 911 Carrera 3.6 liter is up 20hp to 345hp. Output of the 911 Carrera S 3.8 liter is equally impressive, up 30hp to 385hp. With this extra power, the Carrera S Coup now offers a top speed of slightly over 188 mph.
Direct fuel injection also serves to ensure `homogeneous' operation of the power unit with a consistent balance of the fuel/air mixture in the combustion chamber at all times and under all running conditions. Such operation guarantees optimum combustion, maintaining low emissions, without making any particular requirements in terms of fuel quality. Depending on engine load and speed, fuel is injected into the combustion chamber at a pressure of 120-bar. The big advantage is that unlike conventional intake manifold injection, direct fuel injection serves to form the fuel/air mixture directly in the combustion chamber. This better mixes the air and fuel in the cylinder, establishing an important prerequisite for clean and complete combustion.
With the evaporation of fuel reducing the temperature in the combustion chamber, the amount of air ingested may be increased accordingly, helping to improve the cylinder charge and the level of engine power. At the same time, the cooler fuel/air mixture allows a higher compression ratio in the interests of greater efficiency and extra power from less fuel. Thus, the combustion chambers in both the 3.6 and 3.8liter engines now have a compression ratio of 12.5:1, as opposed to 11.3:1 and 11.8:1 respectively on the previous engines.
The new generation 911 is available for the first time with the new Porsche double-clutch transmission. Offering seven forward gears, the new gearbox combines the driving comfort of a torque converter-equipped automatic with the dynamic manual gearshift functionality of a sequential racing gearbox. PDK also boasts an entirely automatic gearshift function, and replaces the Tiptronic S automatic transmission previously offered on the Carrera and Carrera S.
Through its optimised and adaptive gearshift programmes, PDK improves the acceleration of the 911 and reduces fuel consumption to a level even lower than before.
In principle, the PDK consists of a conventional manual gearbox and a hydraulic control system divided into two separate transmission units. Two wet clutches in radial arrangement, controlled hydraulically, and using oil for both cooling and lubrication, form the heart of the transmission. One clutch is for the first transmission unit with the uneven gear ratios (1,3,5,7) and reverse, and the other clutch is for the second transmission unit with the even gears (2,4,6). Via a number of pressure valves, the hydraulic control unit masterminds both the wet clutches and the shift cylinders activating the transmission ratio required.
The gearshift perceived by the driver comes not from the gears actually changing, but from the change of positive clutch engagement. In this case, the clutch on one transmission opens or disengages while the clutch on the other transmission closes or engages in a simultaneous process.
The big advantage is even faster gearshift than with a conventional manual gearbox or torque converter automatic transmission. The gears are already `in mesh' when shifting and the power of the engine need not be interrupted in the process.