Flat engine

A flat engine is an internal-combustion engine with horizontally opposed cylinders arranged on both sides of a central crankshaft. Its low profile and opposing piston motion distinguish it from vertical and V-shaped layouts.

Boxer engine: A flat engine in which each opposing piston pair moves toward and away from the crankshaft together. Its paired piston motion distinguishes the strict boxer layout from other engines called flat.
V engine: An internal-combustion engine whose cylinders are arranged in two banks meeting at an angle. Both layouts use two cylinder banks, but a V engine places them at an angle rather than opposite horizontally.
Porsche 911: A sports car model produced by Porsche with a rear-mounted flat-six engine in most generations. Its long-running flat-six layout is one of the best-known applications of flat engines.
Engine balance: The degree to which engine forces and moments cancel during operation. Opposing piston movement can reduce some vibration forces, though balance depends on configuration.
Crankshaft: A rotating shaft that converts reciprocating piston motion into rotary motion. The cylinders sit on opposite sides of this central shaft.
Inline engine: An internal-combustion engine with cylinders arranged in a single straight bank. An inline engine concentrates cylinders in one row instead of splitting them across the crankshaft.
Subaru: A Japanese automobile manufacturer whose passenger cars are widely associated with horizontally opposed engines. The company adopted flat engines across many vehicle lines, often with all-wheel drive.
Center of gravity: The point at which an object's mass can be treated as concentrated for analyzing its motion. A low-mounted flat engine can lower a vehicle’s center of gravity.
Piston: A cylindrical engine component that moves within a cylinder and transfers combustion force to a connecting rod. Opposing pistons drive the flat engine’s crankshaft from both sides.
Radial engine: A reciprocating engine with cylinders arranged radially around a central crankshaft. Its cylinders radiate around the shaft, unlike the flat engine’s opposed horizontal banks.

Linked from 2 pages

Straight engineCompared with: Its opposing banks lower engine height but broaden the engine.