Mercedes-Benz M100 engine

{{Infobox automobile engine

|name=Mercedes-Benz M100 engine

|image=MB W109 6 3 engine.jpg

|caption=In a Mercedes-Benz 300 SEL 6.3

|manufacturer=Daimler-Benz

|production=1963-1981

|configuration=Naturally aspirated V8

|displacement={{ubl|{{convert|6333|cc|L cuin|1|abbr=on|order=flip}} (1963-1981)|{{convert|6834|cc|L cuin|1|abbr=on|order=flip}} (1975-1981)}}

|bore={{ubl|{{convert|103|mm|in|3|abbr=on|lk=on}} (1963-1981)|{{convert|107|mm|in|3|abbr=on|lk=on}} (1975-1981)}}

|stroke={{convert|95|mm|in|3|abbr=on|lk=on}}

|block=Cast iron

|head=Aluminum

|valvetrain=SOHC

|compression={{ubl|9.0:1 (1963-1981)|8.8:1 (1975-1981)}}

|fuelsystem=Mechanical fuel injection

|management={{ubl|Daimler-Benz designed (1963-1972)| |Bosch K-Jetronic (1973-1981)}}

|fueltype=Gasoline

|oilsystem=Dry sump

|coolingsystem=Water-cooled

|power={{ubl|{{convert|250|PS|kW hp|abbr=on|lk=on}} at 4000 rpm (1963-1981)|{{convert|286|PS|kW hp|abbr=on|lk=on}} at 4250 rpm (1975-1981)}}

|torque={{ubl|{{convert|51|kpm|Nm lbft|abbr=on|lk=on}} at 2800 rpm (1963-1981)|{{convert|56|kpm|Nm lbft|abbr=on|lk=on}} at 3000 rpm (1975-1981)}}

}}

The Mercedes-Benz M100 engine was a {{convert|6333|cc|cuin|1|abbr=on|lk=on}}{{cite web | url=http://jalopnik.com/5273116/engine-of-the-day-mercedes-benz-m100-v8 | title=Engine Of The Day: Mercedes-Benz M100 V8 | publisher=Gizmodo Media Group | work=Jalopnik | date=30 May 2009 | accessdate=16 July 2017 | last=Martin | first = Murilee}} single overhead cam V8 produced by Mercedes-Benz between 1963 and 1981. The successor to the M189 version of the company's venerated {{convert|2996|cc|cuin|1|abbr=on|lk=on}} 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 {{convert|6333|cc|cuin|1|abbr=on|lk=on|}} was chosen to exceed that of the first Rolls-Royce V8 engine with {{convert|6231|cc|cuin|1|abbr=on|lk=on|}} 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 {{convert|6834|cc|cuin|1|abbr=on|lk=on}} for the Mercedes-Benz 450SEL 6.9 (1975-1981) in 1975 and thus exceeded the enlarged Rolls-Royce V8 engine with its {{convert|6750|cc|cuin|1|abbr=on|lk=on}} 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 {{convert|6834|cc|cuin|1|abbr=on|lk=on}} version used a Bosch K-Jetronic Continuous Injection System.

The 6.3 L engine was conservatively rated at {{convert|250|PS|kW hp|0|abbr=on|lk=on}}, with {{convert|51|kpm|Nm lbft|0|abbr=on|lk=on}} of torque helping to compensate for the 2.85 to 1{{cite web|url=https://mercedes-benz-publicarchive.com/marsClassic/de/instance/ko/300-SEL-63.xhtml?oid=4903&relId=1001&resultInfoTypeId=175#prevId=191706845|title=Mercedes-Benz Press Info · page 5 |date=22 February 1968| accessdate=23 May 2025}} final drive ratio necessary for sustained high-speed cruising.

In non-US trim, the larger engine produced {{convert|286|PS|kW hp|0|abbr=on|lk=on}} with {{convert|550|Nm|lbft|0|abbr=on|lk=on}} of torque. The North American version, introduced in 1977, was significantly less powerful at {{convert|250|PS|kW hp|0|abbr=on|lk=on}} and {{convert|488|Nm|lbft|0|abbr=on|lk=on}} 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 {{convert|12500|mi|km|abbr=on|lk=on}}. 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 {{convert|50000|mi|km|abbr=on|lk=on}}.