page_title: Straight-eight engine
section_title: Performance and racing cars
hierarchical_section_title: Straight-eight engine / Performance and racing cars
caption_attribution_description: Deutsch: Alfa Romeo 8C 2300, Baujahr 1932, Motor und Kompressor
context_page_description: The straight-eight engine or inline-eight engine is an eight-cylinder internal combustion engine with all eight cylinders mounted in a straight line along the crankcase. The type has been produced in side-valve, IOE, overhead-valve, sleeve-valve, and overhead-cam configurations.
  A straight-eight can be timed for inherent primary and secondary balance, with no unbalanced primary or secondary forces or moments. However, crankshaft torsional vibration, present to some degree in all engines, is sufficient to require the use of a harmonic damper at the accessory end of the crankshaft. Without such damping, fatigue cracking near the rear main bearing journal may occur, leading to engine failure.
  Although an inline six-cylinder engine can also be timed for inherent primary and secondary balance, a straight-eight develops more power strokes per revolution and, as a result, will run more smoothly under load than an inline six. Also, due to the even number of power strokes per revolution, a straight-eight does not produce unpleasant odd-order harmonic vibration in the vehicle's driveline at low engine speeds.
context_section_description: Despite the shortcomings of length, weight, bearing friction, and torsional vibrations that led to the straight-eight's post-war demise, the straight-eight 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 dual overhead camshaft straight-eight engines in the 1920s and 1930s.
  The Duesenberg brothers introduced the first successful straight-eight racing engine in 1920, when their 3 L engine placed third, fourth, and sixth at the Indianapolis 500. The following year one of their cars won the French Grand Prix, while two others placed fourth and sixth in the race. Based on work the company had done on 16-cylinder aircraft engines during World War I, the overhead camshaft, three-valve-per-cylinder engine produced 115 brake horsepower (86 kW) at 4,250 rpm, and was capable of revving to an astonishing (at the time) 5,000 rpm. No Grand Prix engine before the war had peaked at more than 3,000 rpm.
  Bugatti experimented with straight-eight engines from 1922, and in 1924, he introduced the 2 L Bugatti Type 35, one of the most successful racing cars of all time, which eventually won over 1000 races. Like the Duesenbergs, Bugatti got his ideas from building aircraft engines during World War I, and like them, his engine was a high-revving overhead camshaft unit with three valves per cylinder. It produced 100 bhp (75 kW) at 5,000 rpm and could be revved to over 6,000 rpm. Nearly 400 of the Type 35 and its derivatives were produced, an all-time record for Grand Prix motor racing.
  Alfa Romeo were the first to react to the engineering problems of the straight-eight: in their racing car engines for the P2 and P3 and in their Alfa Romeo 8C 2300/2600/2900 sports cars of Mille Miglia and Le Mans fame the camshaft drive had been moved to the engine centre, between cylinders four and five, thus reducing the aforementioned limitations. The straight-eight was actually built as a symmetrical pair of straight-four engines joined in the middle at common gear trains for the camshafts and superchargers. It had two overhead camshafts, but only two valves per cylinder.
  The Alfa Romeo straight-eight 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. The Alfa Romeo 158/159 Alfetta was originally designed in 1937 and won 47 of 54 Grands Prix entered between 1938 and 1951 (with a six-year gap in the middle caused by the war). By 1951, their 1.5 L supercharged engines could produce 425 bhp (317 kW) at 9,300 rpm, and could rev as high as 10,500 rpm. However, the engines were at the end of their potential, and rule changes for the 1952 season made the Alfettas obsolete.
  Mercedes-Benz would create the last notable straight-eight 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 deadly accident at the 1955 24 Hours of Le Mans. The 300SLR was the final development of the Alfa Romeo design of the early 1930s as not only the camshaft, but now also the gearbox was driven from the engine's centre. Engineers calculated that torsional stresses would be too high if they took power from the end of the long crankshaft, so they put a central gear train in the middle (which also ran the dual camshafts, dual magnetos, and other accessories) and ran a drive shaft to the clutch housing at the rear.
caption: 1932 Alfa Romeo 2,336 cc (142.6 cu in) DOHC Roots supercharged straight-8.
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