Mercedes-Benz M100 engine

The Mercedes-Benz M100 engine was a single overhead cam V8 produced by Mercedes-Benz between 1963 and 1981. The successor to the M189 version of the company's venerated straight-6 M186, it was introduced in the flagship Mercedes-Benz 600. In 1968, it was fitted to the high-performance Mercedes-Benz 300SEL 6.3 sports sedan.

The displacement of was chosen to exceed that of the first Rolls-Royce V8 engine with by approximately 0.1 L. According to applicable rounding rules, this results in to 6.2 L, so Mercedes-Benz also followed the applicable rounding rules and stated 6.3 L.

The engine was enlarged to for the Mercedes-Benz 450SEL 6.9 (1975-1981) in 1975 and thus exceeded the enlarged Rolls-Royce V8 engine with its by approximately 0.1 L. As this Rolls-Royce figure has to be rounded up in accordance with the applicable rounding rules, Rolls-Royce stated 6.8 L, so that Mercedes-Benz felt compelled to round up as well in order to indicate the almost unchanged displacement advantage with the 6.9 L figure. The fact that this was only possible if the applicable rounding rules were not observed was deliberately accepted. This was a remarkable move for a company that was committed to understatement at the time.

The M100 featured a cast iron block, aluminum alloy heads, and aircraft-style sodium-filled valves operating against hardened valve seats. As in all Mercedes-Benz automobile engines, the crankshaft, connecting rods and pistons were forged instead of cast.

Each hand-built unit was bench-tested for 265 minutes, 40 of which were under full load. As introduced, it utilized a mechanical fuel injection system designed and built in-house by Daimler-Benz. The version used a Bosch K-Jetronic Continuous Injection System.

The 6.3 L engine was conservatively rated at , with of torque helping to compensate for the 2.85 to 1 final drive ratio necessary for sustained high-speed cruising.

In non-US trim, the larger engine produced with of torque. The North American version, introduced in 1977, was significantly less powerful at and of torque due to more stringent emissions control requirements.

The "6.9"-liter M100 used a "dry sump" engine lubrication system, which both enhanced longevity and reduced overall engine height. Originally developed for racing as a way to prevent engine oil foaming at high crankshaft speeds, which in turn would create a serious drop in oil pressure, it allowed sustained high speeds at full engine power. The M100 system circulated a massive twelve litres of oil through the engine and a storage tank mounted inside the right front fender, as opposed to the usual four or five litres found in V8s with a standard oil pan and oil pump configuration. The dry sump system also had the benefit of extending the oil change interval to . This, along with hydraulic valve lifters which required no adjusting and special cylinder head gaskets which eliminated the need for periodic retorquing of the head bolts, made the 6.8 nearly maintenance-free for its first .

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