Mercedes-Benz M04 engine
{{Infobox automobile engine
|image =
|name = Mercedes-Benz M04
|manufacturer = Mercedes-Benz
|production = 1927-1928
|configuration = Inline-6
|bore = {{convert|76|mm|in|1|lk=on|abbr=on}}
|stroke = {{convert|115|mm|in|1|lk=on|abbr=on}}
|displacement = {{convert|3.0-3.1|L|cuin|0|lk=on|abbr=on}}
|valvetrain = 12-valve, SOHC, two-valves per cylinder
|power = {{convert|55|hp|kW|0|lk=on|abbr=on}}
|torque = {{convert|119|lb.ft|N.m|0|lk=on|abbr=on}}
|fuelsystem = Carburetor
|fueltype = Gasoline
|compression = 5.0:1
|oilsystem = Dry sump
|weight =
|predecessor = Mercedes-Benz M03 engine
|successor = Mercedes-Benz M09 engine
}}
The Mercedes-Benz M04 engine is a naturally-aspirated, 3.0-liter and 3.1-liter, straight-6, internal combustion piston engine, designed, developed and produced by Mercedes-Benz; between 1927 and 1928.{{Cite web|url=https://sportlichleicht.com/info/engines/m04/|title=Mercedes-Benz M04 Engine|website=Sportlichleicht.com|access-date=10 November 2021}}{{Cite web|url=https://www.car.info/en-se/mercedes-benz/12-55-ps/1255-ps-torpedo-m4-1927-257250/specs|title=Mercedes-Benz 12/55 PS Typ 300 Torpedo Manual, 55hp, 1927|website=Car.info|access-date=10 November 2021}}{{Cite web|url=https://www.autoevolution.com/cars/mercedes-benz-typ-s-w06-1927.html|title=MERCEDES BENZ Typ S (W06) specs & photos - 1927, 1928|website=Autoevolution.com|access-date=10 November 2021}}{{Cite web|url=https://simeonemuseum.org/collection/1927-mercedes-benz-s-type-sportwagen/|title=1927 Mercedes-Benz S-Type Sportwagen|first=William|last=Murphy|date=2 July 2008|website=Simeone Foundation Automotive Museum|access-date=10 November 2021}}{{Cite web|url=https://www.autoevolution.com/cars/mercedes-benz-typ-1255-1460-w03w04w05-1926.html|title=MERCEDES BENZ Typ 12/55 - 14/60 (W03/W04/W05) specs & photos - 1926, 1927, 1928, 1929|website=Autoevolution|access-date=10 November 2021}}{{Cite web|url=https://www.car.info/en-se/mercedes-benz/12-55-ps/1255-ps-torpedo-w04-257199/specs|title=Mercedes-Benz 12/55 PS Torpedo W04|website=Car.info|access-date=10 November 2021}}
M04 engine
The side-valve six-cylinder 2,994 cc engine delivered maximum output of {{Convert|55|PS|kW hp|0|abbr=on}}, but now at the lower engine speed of 3,200 rpm. At the back, however, the final drive ratio was changed from 5.4 :1 to 4.8 : 1, and the listed top speed went up to 108 km/h (67 mph)
Having raised the final drive and the top speed for 1927, the manufacturer now moved to offer a choice of ratios, either reducing it back to 5.4 :1 or raising it further to 5.8 :1. The former ratio was described as the “Flachland” (flat lands) version while the latter as the “Berg” (mountain) version. At the same time a small increase in the cylinder stroke accounted for an increase in overall engine capacity to 3,131 cc. Claimed maximum output was unchanged at {{Convert|55|PS|kW hp|0|abbr=on}}, still at 3,200, although there was a measurable increase in torque.