For the limit of 3 liter supercharged that came in effect for 1938, one V12 was designed, with two generations; the M154 / M163.[9][10][11][12]
Not to Grand Prix rules, but for Voiturette (F2) rules and closely related, was the one-off model made for the 1939 Tripoli Grand Prix, the 1500 cc supercharged V8 Mercedes-Benz W165 which also was run at Indianapolis in the 1940s. The design could have been raced in post war Grand Prix and even in Formula One up to 1951, but Mercedes decided against reviving the old model.
Some of the surviving W154 were entered in 1951 Formula Libre races in Argentina. At the 1952 German Grand Prix, one of the Mercedes 300 SL (W194) entered in the supporting sports car race had a supercharged version of the Mercedes-Benz M194 engine, the M197, which basically was the very last Mercedes-Benz supercharged Grand Prix racing engine.
1934
From 1928 to 1932, the Mercedes-Benz SSK had a supercharged M067,069cc (7.1L)SOHCI6 engine that powered a 3,750lb (1,700kg) car with up to 300hp (220kW). For 1934, the rules for Grand Prix racing cars were simple: a 750kg maximum weight, and not much else.
Despite reducing the engine size by roughly half, with about 3.3 litre in the first version, Daimler engineers soon managed to get more power from the supercharged Straight-8 M25 engine than the maximum 300 hp of the SSK. Staying under the weight limit was a challenge, though, and legend has it that the traditional white paint had to be removed over night after the cars failed scrutineering, giving birth to the Silver Arrows. That moniker was already used in 1932, though.
Development of the chassis and the car, with versions W25AB and W25B, allowed to increase capacity close to 4-litres, and output of 370hp (280kW). The W25B dominated the 1935 Grand Prix season.
1936
The 1936 Grand Prix season was dominated by political turmoil, and by Auto Union, which had its V16 bored out to 6.0 litre and over 500hp, while Mercedes reached the limit of the M25 engines which became unreliable when enlarged to 4.7-litre and 490hp. A DAB V12 engine was tested in a shorter W25K, but it proved too heavy for GP racing, and was used in the high speed Mercedes-Benz W125 Rekordwagen only. Mercedes used the shorter W25K chassis as well as the M25C[13] with over 400hp (300kW), but that was not enough. Mercedes withdrew from GP racing after the August 1936 Swiss Grand Prix to focus on a new car.
With no regulations limiting engine size, other than the 750kg (1,650lb) total car weight limit, Mercedes designed a 5.6-litre engine configured with eight inline cylinders and double overhead camshaft for the W125. Named the M125, the engine was also fitted with a Roots type supercharger producing 632lb⋅ft (857N⋅m) of torque at the start of the season. The engines built varied in power, attaining an output range of 560–640hp (420–480kW) at 5800rpm. Fuel used was a custom mix of 40% methyl alcohol, 32% benzene, 24% ethyl alcohol and 4% gasoline light.[14] The engine weighed 222kg (489lb) - approximately 30% of the total weight of the car, and was mounted in the front of the car.[15]
The W125's supercharged engine, with 8 cylinders in line, bore x stroke of 94.0mm ×102mm (3.7in ×4.0in), displacing 5,662.85cc (345.57cuin), attained an output of up to 595 horsepower (444kW) in race trim. The highest testbed power measured was 637bhp (646PS) at 5,800rpm. It gave 245bhp (248PS) at a mere 2,000rpm.
The W125 was considered the most powerful road racing car ever for about three decades, until large capacity, American-built V8 engines in Can-Am sports cars reached similar power in the late 1960s. In Grand Prix racing itself, the figure was not exceeded until the early 1980s (when Grand Prix racing had become known as Formula One), with the appearance of very powerful turbocharged engines; such as the Renault EF-Type engine, BMW M12/13, and the Ferrari Tipo 021.[16]
1938
The 1938 Grand Prix season saw changes in the rules by the sports governing body AIACR, with the maximum limit on weight being replaced with a maximum limit on engine capacity (3000cc when supercharged, 4500cc without) and a minimum weight for the car being introduced. Thus, the W125 was no longer eligible for entry, and even the 1934 W25A engine was too large for the new rules. Instead, Mercedes-Benz developed a new car, the Mercedes-Benz W154 car based on the chassis design of the W125, with a V12 M154 engine, supercharged 3000cc, after both types had been tested.
The new M154 engine was a 3.0L (2,961.54cc; 180.7cuin) supercharged V12 with bore x stroke of 67.0mm ×70.0mm (2.64in ×2.76in), attaining an output between 425 and 474hp (317 and 353kW). In 1939, the 2-stage supercharged version recorded a testbed power of 476bhp (483PS) at 7,800rpm. Each one of these engines reputedly cost 89,700 German reichsmarks in 1938 (US$949,601 today).
The new car was successful, with the competition also having to comply with the new rules.
1939
For the 1939 Grand Prix season that was not completed, a different body was used, and the M154 engine was replaced by the M163 version. As a result of the new engine number, the 1939 car is often mistakenly referred to as a Mercedes-Benz W163.[17]
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