M137

The W220 S-Class was markedly smaller than the W140 it replaced, and its engine compartment had been dimensioned around the M113 V8; the decision to offer a twelve at all came late in the program. So the M137 was designed small. Cylinder spacing was held to 90 mm, the layout went slightly long-stroke, and in place of the M120's four camshafts and 48 valves it borrowed the architecture of the M112 and M113 — one camshaft per bank, three valves per cylinder, twin plugs fired in sequence. At 220 kg it was 80 kg lighter than its predecessor.

Its novelty was cylinder deactivation. At light load below 3,000 rpm, split rocker fingers uncoupled by hydraulic pistons held the left bank's valves shut, so all twelve pistons kept moving but only six cylinders worked — fewer pumping losses, and better filling for the ones still firing. AMG took it out to 6,258 cc and 443 PS for the S 63, the CL 63 and a very few G 63s from autumn 2001, then dropped it within a year for the supercharged 5.5-liter V8 that beat it on both power and torque. Built at Berlin-Marienfelde; replaced by the M275 in 2002.