OM606

It replaced the OM603 in 1993 as the six of the four-valve family: twin camshafts, split intake ports, and a closed-deck iron block carrying a forged crankshaft on seven main caps. Naturally aspirated engines ran a 25:1 compression ratio for 136 PS in the W124 E 300 Diesel. From 1996 the turbocharged versions were intercooled, which the OM603 never had been, and made 177 PS with 330 N·m held from 1,600 rpm in the E 300 Turbodiesel, the S 300 Turbodiesel and the G 300 Turbodiesel.

Its afterlife is the reason the code is familiar. Injection stayed mechanical — a Bosch inline pump, electronically governed on most versions — so fuelling is raised by fitting larger pump elements rather than by rewriting a common-rail map, and the bottom end absorbs the result. Builders reckon on 500 to 650 hp without opening the engine, going to forged rods and a pinned crankshaft and intake camshaft above that. That combination of a mechanical pump and a crankshaft that tolerates abuse made it one of the most swapped diesel engines in the world, and it is a large part of why the common-rail OM613 that replaced it has no comparable following.