The Mercedes D.IVa was a German six-cylinder, water-cooled, inline engine developed in 1917 for use in aircraft and built by Daimler Motoren Gesellschaft (DMG).

[1] The D.IVa replaced the failed Mercedes D.IV inline eight-cylinder engine.

Unlike most German designs, the D.IVa was relatively advanced, including four valves per cylinder actuated by a SOHC valvetrain, the same "single-camshaft" arrangement that had also been used on the earlier two-valve per cylinder D.I through D.IIIa powerplants.

For instance, the carburetor was placed behind the engine, feeding fuel to the cylinders via a long tubular intake manifold.

Two versions of the engine were produced in mirror copies, running in opposite directions.