Flat-six engine

The disadvantages are a large width (which can limit the maximum steering angle when used in a front-engined car), a large intake manifold being required when a central carburetor is used, and duplication of the inlet and outlet connections for water-cooled engines.

Several other car manufacturers, including Subaru, have produced flat-six engines at times.

(The moment is not quite zero in practice because each cylinder pair is offset slightly from the other, or else they would clash at the crankshaft.)

Several manufacturers use the letter O in their model codes for flat-layout engines as a designation for “opposed” cylinder layouts.

The smaller frontal area compared with a radial engine also results in less drag.

Several examples of the Pietenpol Air Camper homebuilt monoplane aircraft have used the air-cooled engine from the Chevrolet Corvair compact car.

Although the side-valve format has long been abandoned for most automotive applications because its combustion chamber is a bar to high engine rpm, the massively over-square (1.295:1) D-Motor is a very simple, low-revving, compact, reliable lightweight aero-engine (without the heavy (and bulky) complication of ohv valve-gear).

Reports on this car quote it as being "remarkably silent and smooth running" and "almost total absence of vibration".

[8] Two American manufacturers briefly produced cars with flat-six engines—the 1948 Tucker 48 (water-cooled, based on the Franklin O-335) and the 1960–1969 Chevrolet Corvair (air-cooled).