The straight-eight engine (also referred to as an inline-eight engine; abbreviated I8 or L8) is a

piston engine A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common fea ...

with eight cylinders arranged in a straight line along the crankshaft. The number of cylinders and perfect primary and secondary engine balance resulted in smooth running, however there are several downsides relating to the significant length of the engine. Straight-eight engines were popular in luxury cars and racing cars in the 1920s to 1940s. During the 1950s, straight-eight engines were largely replaced by the more compact

V8 engine A V8 engine is an eight- cylinder piston engine in which two banks of four cylinders share a common crankshaft and are arranged in a V configuration. The first V8 engine was produced by the French Antoinette company in 1904, developed and u ...

design.

Design

Inline 8 Cylinder with firing order 1-4-7-3-8-5-2-6

A straight-eight can achieve perfect primary balance and secondary balance if an appropriate

firing order The firing order of an internal combustion engine is the sequence of ignition for the cylinders. In a spark ignition (e.g. gasoline/petrol) engine, the firing order corresponds to the order in which the spark plugs are operated. In a diesel engi ...

is used. Like most other engines, torsional vibration of the crankshaft requires that a harmonic damper is installed on the crankshaft. at the accessory end of the crankshaft. As per other engines with 8 cylinders, the power delivery is smoother than engines with fewer cylinders. In the early 20th century, these smoothness characteristics made straight-eight engines a common choice for luxury cars and racing cars. A key downside of a straight-eight engine is that its length demanded the use of a long engine compartment, which made it largely unsuitable for modern vehicles. The length of both the crankshaft and

camshaft A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition systems ...

can result in a phenomenon referred to as "crankshaft whip", whereby the

centrifugal force In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is parallel ...

on the crank throws at high engine speeds (RPM), can cause physical contact between the

connecting rod A connecting rod, also called a 'con rod', is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the cranksha ...

s and crankcase walls, leading to the engine's destruction. Due to these issues, straight-eight engines have been replaced by the shorter (but wider)

layout.

Usage in military vehicles

Several straight-eight engines were used in

World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...

,, such as the Mercedes D.IV (however this engine was replaced by a six-cylinder engine in 1917, due to issues with the long crankshaft). Advantages of the straight-eight engine for aircraft applications included the aerodynamics of a narrow engine, and the lack of counterweights on the crankshaft. In 1927, the British

R101 R101 was one of a pair of British rigid airships completed in 1929 as part of a British government programme to develop civil airships capable of service on long-distance routes within the British Empire. It was designed and built by an Air Mi ...

experimental airship was powered by five Beardmore Tornado diesel straight-eight engines. These engines were intended to give an output of at 1,000 rpm but in practice had a continuous output rating of only at 900 rpm."Boulton and Paul - the R101."
''norfolkancestors.org.'' Retrieved: 27 August 2010. The airship project was cancelled in 1931, following a crash on its maiden voyage. From the mid 1940s to the 1960s, several British Army tanks and other wheeled vehicles were powered by Rolls-Royce B80 straight-eight petrol engines. The B80 engine was also used in the Rolls-Royce Phantom IV luxury car, 18 of which were produced from 1950-1956.

Usage in passenger cars

The first documentation of a straight-eight design was in 1903 by French company Charron, Girardot et Voigt, however the engine was not built. The first production car to use a straight-eight engine was the 1919 Isotta Fraschini Tipo 8 Italian luxury car, which was powered by a 5.9 litre

overhead camshaft An overhead camshaft (OHC) engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion ...

petrol engine. Approximately 1,380 Tipo 8 cars were produced from 1919-1924. In contrast, the first

was built in 1904 and by 1918 several manufacturers were producing V8 engines in significant quantities. The 1920-1923 Leyland Eight British luxury car was powered by a 6.9 litre (later enlarged to 7.3 litres) overhead camshaft straight-eight engine. Histomobile: Leyland - 1920s The 1921-1928 Duesenberg Model A American luxury car was powered by a 4.3 litre overhead camshaft straight-eight engine and is considered the first mass-production car to use a straight-eight engine. During the 1930s, various luxury and performance cars used straight-eight engines, including double overhead camshaft engines used in the

Bugatti Type 35 The Bugatti Type 35 was the most successful of the Bugatti racing models. Its version of the Bugatti arch-shaped radiator that had evolved from the more architectural one of the Bugatti Type 13 Brescia, was to become the one that the marque is ...

and Duesenberg Model J and single overhead camshaft engines produced by Daimler, Mercedes-Benz, Isotta Fraschini, Alfa Romeo, Stutz Motor Company, Stearns-Knight and Packard. From

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

onwards, production of straight-8 engines rapidly declined and the layout was largely obsolete by the mid 1950s. In the United States, most manufacturers switched to

s In Europe, most manufacturers downsized to four-cylinder and six-cylinder engines, while the few remaining eight-cylinder engines used a V8 layout.

Engines produced in the United States

Straight-eight engines built in the United States include: * 1921-1927 Duesenberg 260 cuin engine * 1924-1927 Lycoming ''Model H'' 225 cuin and ''Model 2H'' 228 cuin engines - used by Auburn Automobile * 1928-1932 Lycoming 298 cuin engine - used in the Auburn Speedster and the front-wheel drive Cord L-29Wise, David Burgess. "Cord: The Apex of a Triangle", in Northey, Tom, ed. ''World of Automobiles'' (London: Orbis, 1974), Vol. 4, pp.435-436. * 1928-1937 Duesenberg 420 cuin engine * 1928-1941 Studebaker 221 and 313 cuin engines - used in the President,

Commander Commander (commonly abbreviated as Cmdr.) is a common naval officer rank. Commander is also used as a rank or title in other formal organizations, including several police forces. In several countries this naval rank is termed frigate captain ...

and

Dictator A dictator is a political leader who possesses absolute power. A dictatorship is a state ruled by one dictator or by a small clique. The word originated as the title of a Roman dictator elected by the Roman Senate to rule the republic in ti ...

cars * 1930-1939 Hudson 219 cuin flathead engine * 1930-1942 Nash 322 cuin twin-ignition engine - used in the Nash Ambassador * 1930-1952 Chrysler Straight-8 flathead engine * 1931-1934 Reo Royale 8 engine * 1931-1953 Buick straight-8 overhead valve engine * 1932-1949 Oldsmobile Straight-8 flathead engine * 1933-1954 Pontiac Straight-8 flathead engine Chevrolet, Cadillac and Ford did not produce straight-8 engines, instead using V8 engines for their cars.

Usage in racing cars

In 1920, the American Duesenberg Automobile and Motors Company produced a 3 litre straight-eight engine which finished in third, fourth, and sixth place at the

Indianapolis 500 The Indianapolis 500, formally known as the Indianapolis 500-Mile Race, and commonly called the Indy 500, is an annual automobile race held at Indianapolis Motor Speedway (IMS) in Speedway, Indiana, United States, an enclave suburb of India ...

. The following year one, Duesenberg cars placed first, fourth and sixth at the

French Grand Prix The French Grand Prix (french: Grand Prix de France), formerly known as the Grand Prix de l'ACF (Automobile Club de France), is an auto race held as part of the Fédération Internationale de l'Automobile's annual Formula One World Champions ...

. The engine had an overhead camshaft, three valves per cylinder, produced and could achieve engine speeds of up to 5,000 rpm - significantly higher than the 3,000 rpm speeds of engines a few years earlier. The 1924

grand prix racing car was powered by a 2 litre overhead camshaft engine with three valves per cylinder. This engine produced at 5,000 rpm and could be revved to over 6,000 rpm. The ''Type 35'' won over 1000 races, one of the most successful racing cars of all time. Almost 400 of the Type 35 and its derivatives were produced, which is a record number for grand prix racing. The Alfa Romeo P2 grand prix racing car was introduced in 1924, powered by a supercharged straight-eight engine with twin overhead camshafts but only two valves per cylinder. In order to minimise the straight-eight's common issues of relating to twisting of the camshaft and crankshaft, the camshaft drive was located in the centre of the engine, between cylinders four and five. Upgraded versions of this engine were also used in the 1932-1935 Alfa Romeo P3 grand prix racing car, various Alfa Romeo 8C models of racing cars from 1930-1939 and the 1937-1951 Alfa Romeo 158/159 Alfetta grand prix racing car. The 158 and 159 models were highly successful over a long period, winning 47 of 54 races 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 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. One of the last straight-eight racing engines was the Mercedes-Benz M196 engine. It was introduced in the 1954-1955 Mercedes-Benz W196 Formula One racing car, which won 9 of the 12 races it entered. A 3.0 litre version of this engine was used in the 1955 Mercedes-Benz 300SLR sports racing car, which caused Mercedes-Benz to withdraw from motorsport for 30 years due to the 1955 Le Mans disaster. The M196 used camshafts powered from the centre of the engine (as per Alfa Romeo's straight-eight racing engine), along with the

magneto A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...

s and other accessories. Most significantly, the engine's power output (from the crankshaft) was taken from the centre of the engine, with a driveshaft used to transfer power to the clutch located at the rear of the engine.

References