A V20 is an internal combustion engine in V configuration, having 20 cylinders. Engines of this number of cylinders are not common.
A V20 configuration is used by several large diesel engines.
In railroad locomotive use, V20 engines were used in the 1960s vintage EMD SD45, which was fitted with a 20-cylinder EMD 645E3 engine. That engine's so named because 645 is the displacement in cubic inches -- per cylinder. 12900 cubic inches in total, or just over 211 litres. The 20-cylinder version of the 645E3 produces 3600 hp (2684 kW) in turbocharged form.
V20 diesel engines have also been used in marine applications; Mercedes-Benz has produced one such.