Which Mercedes-Benz engine family was used in the Audi F103 series?

The Audi F103 series used the Mercedes-Benz M118 engine family.

The M118 was a four-stroke, inline-four engine developed by Daimler-Benz and used exclusively across the F103 range. It replaced the DKW F102’s two-stroke powerplant, allowing Auto Union to present the cars as modern Audi models rather than DKWs. The engine was mounted longitudinally in the F103’s front-wheel-drive layout.

M118 versions displaced roughly 1.5 to 1.8 litres and powered models including the Audi 72, Audi 80, Audi Super 90, Audi 75 and Audi 60. The engine’s unusual “medium-pressure” design used high compression ratios and carefully shaped intake passages to promote mixture swirl and efficient combustion.

The name can be misleading because the engine is closely associated with Audi in applications, yet its origins were at Mercedes-Benz. Daimler-Benz had developed it during a military-engine project that did not reach production. After Daimler-Benz sold Auto Union to Volkswagen, the engine became central to Audi’s transition from two-stroke DKW engineering to four-stroke Audi cars.