Mercedes-Benz M186 engine

The 3.0–litre (2,996 cc (3.0 L; 182.8 cu in)) M186 was introduced in 1951 for use in the company's flagship 300 "Adenauer" (W186) four-door saloon. It had a slightly under-square bore and stroke of 85 mm × 88 mm (3.35 in × 3.46 in), featured an overhead cam, and an aluminum head with an innovative 30-degree diagonal head-to-block joint that allowed for oversized intake and exhaust valves. Designed to give reliable service under prolonged hard use, the engine featured deep water jackets, thermostatically controlled oil cooling, copper-lead bearings, and a hardened crankshaft. Fitted with twin downdraft Solex carburettors it produced 115 bhp (117 PS; 86 kW)[4] at a 6.4:1 compression ratio.

The W188 300 S coupé/cabriolet was released in 1952 with the M188 variant, being fed by triple downdraft Solex carburettors and producing 150 hp (112 kW) at 5000 rpm and 7.8:1 compression ratio.

The first M189 appeared in the 300d pillarless limousine of 1957, three years after the M198. Rather than using the M198's high-strung Bosch mechanical direct fuel-injection, it used a Bosch indirect fuel injection system to up performance from the underpowered M186 to 180 PS (132 kW; 178 hp) at 5500 rpm.[5] The engine then appeared in 1961 in the Mercedes-Benz W112 300SE and its long wheelbase derivative (also called 300SE; the SEL nomenclature would first be used on the subsequent W109 LWB sedans) two years later. From 1964, power output was 170 hp (127 kW). The final incarnation of the M189 was in the W108 300SEb and W109 300SEL of 1965–1967, producing 170 hp (127 kW).

The M194 engine was developed in 1952 for the W194 300SL racer. Only 10 were made, the first three producing around 170 kW (228 hp), while the remaining seven put out around 180 kW (241 hp).[6]

Like the W188 used in the ultra-exclusive 300 S coupé/cabriolet, the M194 was outfitted with three two-barrel Solex carburetors.[7] Similar to the M198 used in the production 300SL, the engine is titled 50 degrees to the left in order to reduce the height of the hood, and uses a dry sump lubrication system instead of an oil pan and reservoir.[8] It is also mounted behind the front axle for better weight distribution.[9]

The M198, with its distinctive massive sand-cast aluminum intake manifold

The high-performance, fuel-injected M198 was created in 1954 for the first generation of the 300SL, known colloquially as the "Gullwing". To fit under its low profile hood the engine was tilted 50-degrees to the left.[10][11] The result for the car was aerodynamic efficiency, and an enormous sand-cast aluminum intake manifold that stretched across the engine's entire breadth.[12] In order to deliver track-ready performance, race-derived features were built in, including a dry sump lubrication system and Bosch mechanical direct fuel-injection, one of the first production cars with fuel injection. This engine produced 215 PS (158 kW; 212 hp) DIN net at 5,800 rpm and 275 N⋅m (203 lb⋅ft) DIN net of torque at 4,600 rpm[1] and 243 PS (179 kW; 240 hp) net (brake hp) at 6,100 RPM and 294 N⋅m (217 lb⋅ft) net torque at 4,800 RPM. An optional high-performance "Sport" camshaft was also available. This was the only available configuration for the Roadster version of the 300 SL when it made its debut in 1957.[1] Production ended in 1964.

A significantly detuned direct-injection, dry sump oil system engine was used in the late W188 300 Sc of 1955 to 1958 producing 175 hp (130 kW) at 5400 rpm and 8.55:1 compression ratio