Mercedes-Benz M15 engine
{{Infobox automobile engine
|image =
|name = Mercedes-Benz M15
|manufacturer = Mercedes-Benz
|production = 1931-1936
|configuration = Inline-6
|bore = {{convert|65|mm|in|1|lk=on|abbr=on}}
|stroke = {{convert|85|mm|in|1|lk=on|abbr=on}}
|displacement = {{convert|1.7|L|cuin|0|lk=on|abbr=on}}
|valvetrain = 12-valve, SOHC, two-valves per cylinder
|power = {{convert|32|hp|kW|0|lk=on|abbr=on}}
|torque = {{convert|52.5|lb.ft|N.m|0|lk=on|abbr=on}}
|fuelsystem = Carburetor
|fueltype = Gasoline
|compression = 5.75:1
|oilsystem = Dry sump
|weight =
}}
The Mercedes-Benz M15 engine is a naturally-aspirated, 1.7-liter, straight-6, internal combustion piston engine, designed, developed and produced by Mercedes-Benz; between 1931 and 1936.{{Cite web|url=https://sportlichleicht.com/info/engines/m15/|title=Mercedes-Benz M15 Engine|website=Sportlichleicht.com|access-date=10 November 2021}}{{Cite web|url=https://www.automobile-catalog.com/curve/1931/23645/mercedes-benz_170.html|title=Horsepower and Torque curve for 1931 Mercedes-Benz 170 (man. 4) offered since mid-year 1931 for Europe|website=Automobile-catalog.com|access-date=10 November 2021}}{{Cite web|url=https://www.automobile-catalog.com/make/mercedes-benz/170_w-15/170_w-15_cabriolet_c/1934.html|title=1934 Mercedes-Benz 170 W15 Cabriolet C full range specs|website=Automobile-catalog.com|access-date=10 November 2021}}
M15 Engine
The car was powered by a six-cylinder 1,692 cc engine:The actual cc was 1692 cc but the Steur cc (tax engine size) was 1680cc. Annual car tax in Germany was charged between 1928 and 1933 according to engine size but, presumably in order to simplify their calculations, the German Finance Office applied roundings in deriving the engine size from the cylinder dimensions with the result that tax cc differed slightly from actual cc. Modern sources sometimes confuse the two figures.Oswald, p. 532 maximum power was set at {{convert|23.5|kW|PS hp|0|abbr=on}} at 3,200 rpm. The engine featured central lubrication and the water-based cooling system for the engine employed both a pump and a thermostat. Power was transmitted to the rear wheels via what was in effect a four-speed manual transmission, on which the top gear operated as a form of overdrive. Third gear used the 1:1 ratio conventionally used by a top gear, and there was a fourth gear with a ratio of 1 : 0.73. Fuel economy was quoted as {{convert|11|L/100 km }} and top speed 90 km/h (56 mph), which combined to represent a competitive level of performance in the passenger car market of that time.