A flat-eight engine, also known as a horizontally opposed-eight, is an eight-cylinder piston engine with four cylinders on each side of a central crankshaft. A flat-eight engine which uses a boxer configuration, where each pair of opposed cylinders moves inwards and outwards at the same time, is called a boxer-eight engine. Flat-eight engines are less common than V8 engines, however they have been used at times in automobiles, including various Porsche racing cars through the 1960s. They have also occasionally been used as aircraft and marine engines.