More power from a Porsche is not a new story. But more power and better fuel consumption is, and that is what we have in the latest Porsche 911 Carrera and Carrera S.
Direct injection boosts power and economy
Porsche has followed the trend in adopting direct fuel injection for the 3.6 and 3.8 liter engines in all 911s. The result is that power is increased by 20 bhp to 345 bhp on the 3.6 liter unit. Output of the 911 Carrera S 3.8-litre power unit is up by 30 bhp to 385 bhp – over 100 bhp per liter. With this extra power, the Carrera S Coupé now has a top speed of 188 mph.
The advantages of direct injection are that:
• The fuel is injected directly where it burns best in the combustion chamber;
• The air is largely unthrottled, so more can get into the cylinders;
• Because the fuel is cooler when it enters the chamber, and can be burnt more efficiently, a higher compression ration can be used.
Higher compression ratio raises efficiency
The compression ratio of both new engines is 12.5:1 – unthinkable just a few years ago – instead of 11.3:1 on the 3.6 liter, and 11.8:1 on the 3.8 liter unit.
Coupled to double-clutch transmission
You can use this extra power more effectively than in the past, because you can choose the latest transmission from Weissach – the double-clutch seven-speed sequential box.
Like most other double-clutch units, Porsche's can be used as an automatic or manual, and so replaces the Tiptronic S box with torque converter, and this change alone makes quite a difference to the fuel consumption – by about 13 percent, says Porsche.
Like other dual-clutch gearboxes, the Porsche unit has three shafts, with 1, 3, 5 and 7 gears on one layshaft, and 2, 4 and 6 on the other. There are also two clutches, of course, one controlling each layshaft. When you shift up with this system, one clutch is disengaged as the other one is engaged at the same time, so gear shifting is much faster than with either a torque converter or manual box – 60 per cent faster than the auto, in fact.
Incidentally, this is not Porsche's first dual-clutch transmission. They used an earlier version in racing back in the 1980s. Shifts with these systems are smoother than with an automated conventional box – as used by Ferrari on most models and by Lamborghini – and is definitely the way to go.
Fuel consumption and CO2 emissions reduced
Thanks to the DI engine and the new transmission, fuel consumption and CO2 emissions are reduced – by up to 15 percent, which is an impressive improvement. Moreover, the performance is improved by quite a margin: the Carrera S Coupé sprints from zero to 60 mph in 4.4 seconds, which is 0.2 seconds faster than with a manual six-speed gearbox and 0.8 seconds quicker than with Tiptronic S.
Porsche's stability control system (PSM) is still standard on the new 911. Now, though, it also includes the Brake Pre-Filling and Brake Assistant functions which ensures faster and more powerful braking response when required.
Although the 997 version of the 911 remains much as before apart from the power train, it does get new 18- and 19-inch wheels, and LED daytime driving lamps and Bi-Xenon headlamps as standard.
