M152

By 2011 Affalterbach had made its choice: the M157 biturbo was spreading through the 63 badges and natural aspiration was on the way out. The M152 was that engine with the blowers deleted and the compression raised to 12.6:1 — same displacement, bore, stroke, cylinder offset, direct injection and stop-start, but new cylinder heads, new intake ducting, a modified valve drive, an adapted oil supply and a different crankcase. Dry mass came to 187 kg. Fritz Eichler, who ran AMG powertrain development, presented it that summer; it reached the road in the R172 SLK 55 AMG.

Its party trick came from Formula 1. AMG Cylinder Management shut off cylinders two, three, five and eight under partial load between 800 and 3,600 rpm whenever the driver selected the transmission's Controlled Efficiency mode, holding their valves closed so that the four still firing worked at a higher and more efficient load point. Going back to eight took 30 milliseconds. The car used around 30 per cent less fuel than the 5.4-liter SLK 55 before it while making considerably more power — and then, after three years, the turbocharged M177 family swept the argument away.