Flat-6

The flat-6 engine of the Honda Valkyrie motorcycle

A flat-6 is a 6 cylinder configuration of a flat engine. The cylinders are laid horizontally, with three on each side. The movement of the pistons in a horizontal engine is all in the same plane, so it creates less vibration than in a V-configuration engine; particularly one with an odd number of cylinders on each side of the engine, like a V6.

Only a few auto makers have used flat-6 engines, among them Tucker in the 1948 Tucker Sedan, Porsche and Subaru. Citroën developed one for the DS but abandoned it due to numerous problems. In the 1960s, Chevrolet made the Corvair with flat-6 air-cooled engines. The shape of the engine suits it better for rear engine designs, where the low center of gravity is an advantage; in front engine designs the width interferes with the ability of the front wheels to steer.

Lycoming developed a very successful series of flat-6 aircraft engines, as used in many Cessna aircraft.

Flat-6 engines are used in Honda Gold Wing and Honda Valkyrie motorcycles.

Piston engine configurations
Straight	Single, 2, 3, 4, 5, 6, 8, 9, 10, 12, 14
V	2, 4, 5, 6, 8, 10, 12, 16, 20, 24
Flat	2, 4, 6, 8, 10, 12, 16, H
W	8, 9, 12, 16, 18
Other inline	H, VR, Opposed, U (Square), X
Other	Hemi, Radial, Rotary, Pistonless, Deltic, (Wankel)