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 feat ...

with eight cylinders arranged in a straight line along the crankshaft. The number of cylinders and perfect primary and secondary

engine balance Engine balance refers to how the forces (resulting from combustion or rotating/reciprocating components) are balanced within an internal combustion engine or steam engine. The most commonly used terms are ''primary balance'' and ''secondary bala ...

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 us ...

design.

Design

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

A straight-eight can achieve perfect

primary balance Engine balance refers to how the forces (resulting from combustion or rotating/reciprocating components) are balanced within an internal combustion engine or steam engine. The most commonly used terms are ''primary balance'' and ''secondary bala ...

and

secondary balance Engine balance refers to how the forces (resulting from combustion or rotating/reciprocating components) are balanced within an internal combustion engine or steam engine. The most commonly used terms are ''primary balance'' and ''secondary ba ...

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 Torsional vibration is angular vibration of an object—commonly a shaft along its axis of rotation. Torsional vibration is often a concern in power transmission systems using rotating shafts or couplings where it can cause failures if not cont ...

of the crankshaft requires that a

harmonic damper A harmonic damper is a device fitted to the free (accessory drive) end of the crankshaft of an internal combustion engine to counter torsional and resonance vibrations from the crankshaft. This device must be interference fit to the crankshaft in ...

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 syste ...

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 crankshaf ...

s and

crankcase In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, resulting in the fuel/ ...

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,, such as the

Mercedes D.IV The Mercedes D.IV was an eight-cylinder, liquid-cooled inline aircraft engine built by ''Daimler Motoren Gesellschaft'' (DMG) and used on a small number of German aircraft during World War I. Design and development The design was based around ...

(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 M ...

experimental airship was powered by five

Beardmore Tornado The Beardmore Tornado was an eight-cylinder inline diesel aircraft engine built in 1927 by William Beardmore and Company of Glasgow, Scotland, and used in the British R101 airship when petrol engines were thought unsafe in the tropics. The m ...

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 The Rolls-Royce Phantom IV is a British automobile produced by Rolls-Royce. Only eighteen were made between 1950 and 1956. They were only built for buyers whom Rolls-Royce considered worthy of the distinction: the British royal family and heads ...

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 Automobiles Charron, Girardot & Voigt SA (trade mark C.G.V.) was a French motor manufacturer founded by the racing cyclists and motorists Fernand Charron, Léonce Girardot and Émile Voigt. History They opened one of the first French car ...

, however the engine was not built. The first production car to use a straight-eight engine was the 1919

Isotta Fraschini Tipo 8 The Isotta Fraschini Tipo 8 is an Italian luxury car made between 1919 and 1924. History The Isotta Fraschini Tipo 8 is an automobile introduced in 1919 by Isotta Fraschini, a company which underwent a complete change after World War I. Unti ...

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 c ...

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 The Leyland Eight was a luxury car produced by Leyland Motors from 1920 to 1923. The car was designed by the chief engineer of Leyland Motors, J.G. Parry-Thomas and his assistant Reid Railton, and was intended to be the finest car available ...

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 The Duesenberg Model A was the first automobile in series production to have hydraulic brakes and the first automobile in series production in the United States with a straight-eight engine. Officially known as the Duesenberg Straight Eight, t ...

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 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 cha ...

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 The Duesenberg Model J is a luxury automobile made by Duesenberg. Intended to compete with the most luxurious and powerful cars in the world, it was introduced in 1928, the year before the stock market crash that led to the Great Depression. The ...

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 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 The Auburn Speedster was an American car, manufactured by the Auburn Automobile Company of Auburn, Indiana and manufactured in Union City, Indiana. A total of 887 cars were manufactured between 1928 and 1936, across 3 series (1928-1930 with "e ...

and the front-wheel drive

Cord L-29 Cord was the brand name of an American luxury automobile company from Connersville, Indiana, manufactured by the Auburn Automobile Company from 1929 to 1932 and again in 1936 and 1937. The Cord Corporation was founded and run by E. L. C ...

Wise, 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 President most commonly refers to: *President (corporate title) *President (education), a leader of a college or university *President (government title) President may also refer to: Automobiles * Nissan President, a 1966–2010 Japanese ful ...

, Commander 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 time ...

cars * 1930-1939 Hudson 219 cuin flathead engine * 1930-1942 Nash 322 cuin twin-ignition engine - used in the

Nash Ambassador The Nash Ambassador is a luxury automobile that was produced by Nash Motors from 1927 until 1957. For the first five years it was a top trim level, then from 1932 on a standalone model. Ambassadors were lavishly equipped and beautifully construc ...

* 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 Indianap ...

. 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 Championsh ...

. The engine had an overhead camshaft, three valves per cylinder, produced and could achieve engine speeds of up to 5,000

rpm Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensi ...

- 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 The Alfa Romeo P3, P3 monoposto or Tipo B was a classic Grand Prix car designed by Vittorio Jano, one of the Alfa Romeo 8C models. The P3 was first genuine single-seat Grand Prix racing car and Alfa Romeo's second monoposto after Tipo A monopos ...

grand prix racing car, various Alfa Romeo 8C models of racing cars from 1930-1939 and the 1937-1951

Alfa Romeo 158/159 Alfetta The Alfa Romeo 158/159, also known as the ''Alfetta'' (''Little Alfa'' in Italian), is a Grand Prix racing car produced by Italian manufacturer Alfa Romeo. It is one of the most successful racing cars ever; the 158 and its derivative, the ...

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 The Mercedes-Benz W196 was a Formula One racing car produced by Mercedes-Benz for the and F1 seasons. Successor to the W194, in the hands of Juan Manuel Fangio and Stirling Moss it won 9 of 12 races entered and captured the only two world ...

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 1955 Le Mans disaster was a major crash that occurred on 11 June 1955 during the 24 Hours of Le Mans motor race at Circuit de la Sarthe in Le Mans, Sarthe, France. Large pieces of debris flew into the crowd, killing 83 spectators and French ...

. 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