OM628

Audi and BMW had already taken the luxury diesel to eight cylinders, and in 1999 Stuttgart followed with the W220 S 400 CDI. The engineering was shaped by the space it had to fit: rather than the usual 90°, the banks were set at 75°, which left first-order inertia forces to be canceled by a balance shaft in the vee and firing intervals to be evened out by split crankpins. Sand-cast aluminum block and heads, twin cams per bank, common rail and a Garrett GT1749V turbo gave 250 PS and 560 N·m from 1,700 rpm.

It spread to the W163 ML 400 CDI and the G 400 CDI, and in 2003 a 260-PS version went into the W211 E 400 CDI and the facelifted S 400 CDI. Never a high-volume engine, it mattered mostly as a demonstration that a Mercedes flagship could be a diesel without apology — and as the architecture the OM629 inherited wholesale in 2005, keeping the 75° vee, the balance shaft and the split crankpins while adding boost, injection pressure and another seventy horsepower.