A U engine is a piston engine made up of two separate straight engines placed side-by-side and coupled to a shared output shaft. When viewed from the front, the engine block resembles the letter "U".

A V engine, sometimes called a Vee engine, is a common configuration for internal combustion engines. It consists of two cylinder banks—usually with the same number of cylinders in each bank—connected to a common crankshaft. These cylinder banks are arranged at an angle to each other, so that the banks form a "V" shape when viewed from the front of the engine.