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New Mercedes SLK AMG to feature four or eight cylinders

In an effort to reduce fuel consumption, Mercedes-Benz has added direct injection and a cylinder deactivation feature to the new V-8 engine in the 2012 SLK AMG roadster.

2012 SLK AMG engine
The new 5.5-liter V-8 in the 2012 SLK AMG will use cylinder deactivation to improve fuel economy. Mercedes-Benz

Mercedes-Benz's AMG division used to spend all its time figuring out how to get more speed out of standard Mercedes-Benz models. It hand-built 6.3-liter engines and made an automatic transmission that shifted like a dual-clutch automated manual. But now AMG engineers have turned their attention toward efficiency.

The latest engines coming out of the workshop use high-pressure direct injection, and now AMG is adding a new trick, cylinder deactivation, to its efficiency repertoire. The 2012 SLK AMG will be the first car to feature the new cylinder deactivation technology. With it, the engine will cut fuel and spark to four of its eight cylinders when it is running under 3,600rpm. This feature will only take effect if the driver has put the car in C mode, which stands for Controlled Efficiency, according to Mercedes-Benz. The company assures us the transition from four- to eight-cylinder operation will be imperceptible.

The new engine, displacing 5.5 liters, produces 415 horsepower and 398 pound-feet of torque. That represents a 60 horsepower increase over the previous AMG 5.5-liter engine. Mercedes-Benz never offered an SLK AMG featuring the newer 6.3-liter engine V-8.

Cylinder deactivation is not new, seeing use in everything from Cadillacs to Honda minivans. But in its announcement, Mercedes-Benz draws comparisons between its technology and that of Formula 1 race cars, lest we think that AMG has become mundane.

With cylinder deactivation, direct injection, and a new idle-stop feature, which turns off the engine when the car is stopped in traffic, the SLK AMG should get 30 percent better fuel economy than its predecessor. But as EPA test cycles will probably favor four-cylinder operation, the variation between the posted numbers and real-world driving should be substantial.

The 2012 Mercedes-Benz SLK AMG will be unveiled at the 2011 Frankfurt auto show.