STRAIGHT-8

A 'Straight-8' is a straight engine with eight cylinders.
A straight-8 can be timed for total inherent balance, with no unbalanced primary or secondary forces or moments. Although straight-6 engines can also be timed for total inherent balance, a straight-8 has more power strokes per revolution and, as a result, can run more smoothly than a straight-6.

Contents

Inter-war period (1919-1941)

Post-war

Performance and racing cars

Current use

Inter-war period (1919-1941)

Straight-8 engines were used in expensive luxury and performance vehicles before World War II. Bugattis and Duesenbergs commonly used DOHC straight-8 engines. Other noteable straight-8-powered automobiles were built by Mercedes-Benz, Isotta-Fraschini, Auburn, and Cord.
During the early 1930s, the Buick, Oldsmobile, and Pontiac divisions of General Motors all introduced straight-8 engines for the premium vehicles in their respective lines. The Buick straight-8 engine was an overhead valve design, while the Oldsmobile and Pontiac straight-8s were flathead engines. Chevrolet, as an entry-level marque, did not have a straight-8, and Cadillac stayed with their traditional V8 engines. In order to have engines as smooth as the straight-8s of their competitors, Cadillac introduced V12 and V16 engines to the top of their lineup.
Ford never adopted the straight-8, using V8 engines in their entry-level cars and V8 or V12 engines in their Lincoln luxury cars from the 1930s on. Chrysler used a flathead straight-8 in its premium cars, including the Imperial luxury model.

Post-war

Postwar, the main users of the straight-8 were those American luxury and premium cars that were carried over from before the war. However, as styles began to evolve and engines became more highly stressed, the straight-8 fell out of favour. A straight-8 is a very long engine and requires more main bearings to support the crankshaft adequately. In addition, the change in design of cars from a long engine compartment between separate fenders to the modern configuration beginning with the Chrysler Airflow and its shorter engine compartment led to straight-8 engines being phased out of automobile design. Moreover, the quest for higher revs and higher compression ratios showed another weakness of the design: torsional vibrations in the long crank and the long camshafts limited the development of such engines.
Oldsmobile replaced their straight-8 with an overhead valve, high compression V8 in 1949. Buick did the same in 1953, with Pontiac being the last GM marque to do so in 1955.

Performance and racing cars

Despite the shortcomings of length, weight, bearing friction, and torsional vibrations that led to the straight-8's post-war demise, the straight-8 was the performance engine design of choice from the late 1920s to the late 1940s, and continued to excel in motorsport until the mid-1950s. Bugatti, Duesenberg, Alfa Romeo, Mercedes-Benz and Miller built successful racing cars with high-performance double overhead camshaft straight-8 engines in the 1920s and 1930s.
Alfa Romeo were the first to react to the engineering problems of the straight-8: in their racing car engines for the P2 and P3 and in their 8C 2300/2600/2900 sports cars of Mille Miglia and Le Mans fame the camshaft drive had been moved to the engine center between cylinders # 4 and 5, thus reducing the aforementioned limitations.
The Alfa Romeo straight-8 would return after World War II to dominate the first season of Formula One racing in 1950 and to win the second season against competition from Ferrari's V12-powered car in 1951.
Mercedes-Benz would create the last notable straight-8 racing cars in 1955 with the championship-winning W196 Formula One racing car and the 300SLR sports racing car. The 300SLR was famous for Stirling Moss and Denis Jenkinson's victory in the 1955 Mille Miglia but notorious for Pierre Levegh's notorious accident at the 1955 24 Hours of Le Mans. The 300SLR was the final development of the Alfa Romeo design of the early 1930s: essentially a combination of two in-line fours, as not only the camshaft, but now also the gearbox was driven from the engine's center.

Current use

Straight-8s are currently used in luxury coaches, alongside V12 engines. They are generally preferred by coach drivers for their lower fuel consumption and smoother acceleration.