A V20 is an internal combustion engine in V configuration, having 20 cylinders.

Engines of this number of cylinders are not common, but this configuration was used in some large diesel engines. For example, the 1960s vintage General Motors Electro-Motive Division EMD SD45 railroad locomotive was fitted with a 20-cylinder EMD 645E3 engine.

The engine name is based on the displacement of each cylinder in cubic inches. In this case 645 inch³ (10.6 litre) for each of 20 cylinders - a total of 211 L. Power output is 3,600 horsepower (2.7 MW).

V20 diesel engines have also been used in marine applications: Mercedes-Benz has produced one such engine.