Mercedes-Benz has officially confirmed what we told you yesterday: the 2012 SLK55 AMG will get its power from a new, normally aspirated 5.5-liter V-8 engine.
The normally aspirated engine, called M152, is based on the twin-turbo 5.5-liter V-8 that debuted in the CL63 AMG and S63 AMG. This new version eschews forced induction but still produces 415 hp at 6800 rpm and 398 lb-ft of torque at 4500 rpm. Those numbers represent an improvement of 60 hp and 22 lb-ft of torque over the last AMG-fettled SLK.
The keys to the power output are direct-injection, a 12.6:1 compression ratio, fully variable valve timing, and a redline of 7200 rpm. An aluminum crankcase and aluminum pistons help keep the engine’s weight to 412 pounds. As with many modern sports cars, special exhaust valves keep the engine quieter at lower speeds. Above 2000 rpm, the exhaust baffles gradually open to allow for a louder and sportier engine note.
In addition to the power increases over the prior SLK55, Mercedes is proud of the new engine’s fuel savings. The new SLK55 gets a stop/start system and only engages the alternator during engine overrun or braking. Moreover, AMG Cylinder Management can temporarily disable two or four engine cylinders to save fuel. In low-load situations when the engine is turning at between 800 rpm and 3600 rpm, the V-8 can run as a four-cylinder engine to save fuel. The engine will still produce 170 lb-ft of torque and can return to eight-cylinder operation in just 30 milliseconds.
Mercedes also released a blurry photo of the new SLK55. We can see that it differs from the regular SLK-Class with special black wheels, an AMG-style front fascia with aggressive black-painted air intakes, and black hood and fender vents. We presume the car’s suspension and brakes will be upgraded to cope with the additional power. Mercedes hasn’t specified which transmission backs up the new AMG engine, but it’s possible the SLK55 will use the same seven-speed MCT automatic transmission as the C63 AMG.
The 2012 Mercedes-Benz SLK55 AMG will make its debut at the Frankfurt Motor Show in September.