Cylinder cut-out for SLK55

A 310kW, 5.5-litre V8 that uses just 8.5 litres per 100km? That’s what AMG is promising to deliver with a new, non-turbo version of its V8 engine in the upcoming SLK55 AMG.

The new SLK55, which will debut at this year’s Frankfurt Motor Show, will be the first four-cylinder AMG, as well as being faster and more powerful than its predecessor. Confused?

That’s because the SLK55’s engine will take a leaf out of the Mercedes F1 operation’s fuel-saving program with a cylinder deactivation system of its own.

Three years in the making, the M152 engine still produces 310kW – 45 more than its predecessor – but with a whopping 30 percent reduction in fuel economy to take its emissions down to 199 grams of CO2 per kilometre. Astonishingly, it uses a full 3.5 litres/100km less than the outgoing SLK55 AMG.

Closely related to the thumping, 5.5-litre, twin-turbo M157 AMG engine, the M152 ditches the turbos and has been tweaked to be able to shut off its second, third, fifth and eighth cylinders when the engine’s under part load.

While plenty of AMG owners prefer to hear their engines rumble regardless of the throttle opening (and the M152 will always start as a V8), the SLK55 will introduce a Controlled Efficiency button on the transmission tunnel.

With this activated, the M152 will switch from eight cylinders to four, and it will be able to remain as a four cylinder engine from 800rpm to 3600. Even then, it will still have a minimum of 230Nm of torque available at any time, and will switch back to eight cylinders in just 30 milliseconds.

Sixteen hydraulic elements in the new cylinder heads keep the intake and exhaust valves closed for the resting cylinders, while air and fuel is also cut off when the car runs as a four cylinder.

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