A
flat-6 or
horizontally opposed-6 is a
flat engine with six
cylinders arranged horizontally in two banks of three cylinders on each side of a central
crankcase. This should not be confused with the
Opposed-piston engine. The
pistons are mounted to the
crankshaft such that opposing pistons move back and forth in opposite directions at the same time, somewhat like a
boxing competitor punching their gloves together before a fight, which has led to it being referred to as a
boxer engine.