Flat engines

engine configuration with horizontally opposed cylinders, usually a flat-V or boxer configuration

horizontally opposed four-cylinder piston engine

horizontally-opposed two-cylinder piston engine

horizontally opposed 6-cylinder piston engine

horizontally-opposed eight cylinder piston engine

Horizontally-opposed 12-cylinder piston engine

British diesel aircraft engine

horizontally-opposed ten-cylinder piston engine

horizontally-opposed 16-cylinder piston engine

motor vehicle engine

twin-cylinder aircraft piston engine