Straight-8

From Wikipedia, the free encyclopedia

A Straight-8 is a straight engine with eight cylinders.

Unfortunately, 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. Alfa Romeo were the first to react: 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.

Most straight-8 engines were used pre-World War II in expensive luxury and performance vehicles. Bugattis and Duesenbergs commonly used DOHC straight-8 engines. Postwar, the main users of the straight-8 were American luxury cars belonging to Chrysler (flathead configuration) and General Motors owned marques (flathead and OHV configuration), but the straight-8 lost favor by the 1950s, almost universally replaced by the V8. Ford never adopted the straight-8, using V8 or V12 engines from the 1930s on. The legendary Mercedes-Benz 300 SLR, winner of the 1955 Mille Miglia with Stirling Moss behind the wheel and Denis Jenkinson as his navigator used a 3 liter Straight-8 producing 290hp. This was the final development of the ALFA design of the early 1930: 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.

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
W	8, 9, 12, 16, 18
Other inline	H, VR, Opposed, U (Square), X
Other	Radial, Rotary, Pistonless (Wankel)