The Mercedes-Benz SLK55 AMG to be revealed at this year’s Frankfurt Motor Show will see the introduction of a new 5.5-litre AMG engine with cylinder deactivation technology.

Boasting 416bhp and 398lb ft, the naturally aspirated V8 should allow the SLK55 to crack 60mph in under 5 seconds. The hand-built block is the same engine found in the CLS63 and E63 AMG models, albeit with the twin-turbos removed. This not only allows Mercedes’ in-house tuning company to shoehorn it into the compact roadster’s package, but also serves to prevent the SLK being faster than its bigger brother, the SL.

Mercedes has made great strides with the hot SLK’s fuel economy; the new car has a combined economy of 33.2mpg, a 30% improvement over the previous model. CO2 emissions are 199g/km, making the SLK55 the first ever AMG model to drop below the 200g/km barrier. "We want to be the best in each discipline," chairman of AMG Ola Källenius says. “This should apply not only to power and performance, but also to consumption.” Källenius proudly reveals that the 5461cc motor is the most efficient eight-cylinder engine in the world.

The dramatic improvement in economy is largely due to the AMG Cylinder Management system, which shuts down four of the eight cylinders when the engine is operating at low loads. Although not a completely new technology – Mercedes briefly used it in the CL600 and S600 in 2001 – Källenius has overseen its development during his 10-year stint in charge of Mercedes’ F1 engines department. The resting cylinders can now be reactivated within 30 milliseconds, and AMG engine boss Friedrich Eichler claims the transition is so smooth that even professionals can barely feel the transition. Mercedes says its real-world tests have indicated that the engine spends roughly half its time in four-pot mode.

A new sports exhaust system complements the V8’s Jekyll and Hyde personality. Two independent silencer flaps keep the exhaust note civilised at low loads and beneath 2000rpm, opening to give the SLK55 a louder sound when the driver presses on. Fuel injection and standard start/stop technology assist the new car’s quest for fuel efficiency. In the UK, the SLK55 AMG is expected to have a retail price of around £55,000 when it reaches showrooms early next year.

Mercedes AMG vehicles can be found at Classic Driver Car Market.

Text: Joe Breeze
Photos: Mercedes-Benz