The straight-five engine (also referred to as an inline-five engine; abbreviated I5 or L5) is a

piston engine A reciprocating engine, more often known as a piston engine, is a heat engine that uses one or more Reciprocating motion, reciprocating pistons to convert high temperature and high pressure into a Circular motion, rotating motion. This article ...

with five cylinders mounted in a straight line along the

crankshaft A crankshaft is a mechanical component used in a reciprocating engine, piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating Shaft (mechanical engineering), shaft containing one or more crankpins, ...

. Although less common than

straight-four engine A straight-four engine (also referred to as an inline-four engine) is a four-cylinder Reciprocating engine, piston engine where cylinders are arranged in a line along a common crankshaft. The majority of automotive four-cylinder engines use a ...

s and

straight-six engine A straight-six engine (also referred to as an inline-six engine; abbreviated I6 or L6) is a piston engine with six cylinders arranged in a straight line along the crankshaft. A straight-six engine has perfect primary and secondary engine balanc ...

s, straight-five engine designs have been used by automobile manufacturers since the late 1930s. The most notable examples include the Mercedes Benz's diesel engines from 1974 to 2006 and Audi's petrol engines from 1979 to the present. Straight-five engines are smoother running than straight-four engines and shorter than straight-six engines. However, achieving consistent fueling across all cylinders was problematic prior to the adoption of

fuel injection Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of a fuel injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines. All c ...

Characteristics

Straight-five engines are typically shorter than

s, making them easier to fit transversely in an engine bay. They are also smoother than straight-four engines, and are narrower than

V engine A V engine, sometimes called a Vee engine, is a common configuration for internal combustion engines. It consists of two cylinder banks—usually with the same number of cylinders in each bank—connected to a common crankshaft. These cylinder ...

s and

flat engine A flat engine is a piston engine where the cylinders are located on either side of a central crankshaft. Flat engines are also known as horizontally opposed engines, however this is distinct from the less common opposed-piston engine design, ...

Engine balance and vibration

Five-cylinder engines have a

with 72 degree angles. Amongst

four-stroke engine A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either directi ...

s, an advantage of engines with five or more cylinders is that the power strokes are overlapping if the engine has an even firing order. A disadvantage of the odd number of cylinders in a straight-five engine is it results in imperfect primary and secondary

engine balance Engine balance refers to how the inertial forces produced by moving parts in an internal combustion engine or steam engine are neutralised with counterweights and Balance shaft#Overview, balance shafts, to prevent unpleasant and potentially dam ...

, unlike a

which has perfect primary and secondary balance. Counterweights on the crankshaft can be used to counteract some amount of these vibrations. This method is also used in

s.Robert Bosch GmbH, ''Bosch Automotive Handbook, 6th edition'' p. 459–463, Professional Engineering Publishing 2004, .

Firing order

Most

four-stroke A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either directio ...

straight-five engines use a firing order of 1-2-4-5-3. This firing order results in the minimal primary (crank speed) rocking couple, and is used by the Volvo Modular engine, VW/Audi straight-five engine, General Motors Atlas engine and Honda G engine. Straight-five engines typically have a 72 degree crankshaft design. All

two stroke A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes of the piston, one up and one down, in one revolution of the crankshaft in contrast to a four-stroke engine which re ...

straight-five engines are limited in having a single firing order for a given crank configuration; because a complete cycle occurs every 360 degrees, there is no chance to share piston phases without having simultaneous ignitions, so the straight-five is at no disadvantage in this case. Some two-stroke

outboard engine An outboard motor is a propulsion system for boats, consisting of a self-contained unit that includes engine, gearbox and propeller or jet drive, designed to be affixed to the outside of the transom. They are the most common motorised method ...

s, e.g. the ''Mercury Marine Force 150'' engine use a firing order of 1-5-2-3-4.

Carburettors and fuel injection

The use of straight-five

petrol Gasoline (North American English) or petrol ( Commonwealth English) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When formul ...

engines in mass production cars only became truly viable with the advent of reliable

. This is because of the unavoidable problems of a

carburettor A carburetor (also spelled carburettor or carburetter) is a device used by a gasoline internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the Vent ...

supplying an odd number of cylinders and the length of the inlet

manifold In mathematics, a manifold is a topological space that locally resembles Euclidean space near each point. More precisely, an n-dimensional manifold, or ''n-manifold'' for short, is a topological space with the property that each point has a N ...

between the carburetor varying greatly between cylinders at the ends of the engine and those nearer the carburetor. Unlike other engine layouts, these problems are not easily solved by using multiple carburettors.

Diesel engine The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to Mechanics, mechanical Compr ...

s have always used fuel injection, therefore large displacement straight-five diesel engines were commonly seen decades before straight-five petrol engines.

Usage in automobiles

Diesel engines

The 1938

Lancia 3Ro The Lancia Ro, Lancia Ro-Ro and Lancia 3Ro were 4x2 heavy trucks built by Italian manufacturer Lancia from the 1930s through the 1940s for military and civilian use. The 2-cylinder diesel Ro was produced from 1933 to 1939, the 3-cylinder diesel ...

trucks introduced a straight-five diesel engine to replace the previous straight-three engine. Built for the Italian and German armed forces during World War II and later for civilian usage, the truck remained in production until 1950. The first mass-production straight-five passenger car engine was the 1974 Mercedes-Benz OM617, a

naturally-aspirated A naturally aspirated engine, also known as a normally aspirated engine, and abbreviated to N/A or NA, is an internal combustion engine in which air intake depends solely on atmospheric pressure and does not have forced induction through a turboc ...

engine introduced in the ''Mercedes-Benz 300D (W114/W115)'' models. In 1978, a

turbocharged In an internal combustion engine, a turbocharger (also known as a turbo or a turbosupercharger) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake air, forcing more air into the ...

version was introduced in the ''Mercedes-Benz 300SD Turbo'' models. Mercedes-Benz continued to produce straight-five engines for the next 28 years, until the Mercedes-Benz OM647 engine ended production in 2006. In 1978, the Audi 2.0 R5 D engine was introduced in the ''Audi 100'' sedan. In 1983, a turbocharged version was introduced, initially for the U.S. market Audi 100. Several Volvo cars were produced with Audi straight-five diesel engines, prior to the introduction of the Volvo D5 turbo-diesel engine; this engine was produced from 2001 to 2017 and was used in several diesel hybrid applications (marketed as "twin engine" models). Other mass-production straight-five diesel engines include the 1999–2001 VM Motori 531 turbo-diesel engine, the 1998–2007 Land Rover Td5 turbo-diesel engine, the 2006–2019 Ford Duratorq 3.2 turbo-diesel engine and the 1998–2009 Fiat JTD 2.4 turbo-diesel engine.

Petrol engines

Henry Ford Henry Ford (July 30, 1863 – April 7, 1947) was an American Technological and industrial history of the United States, industrialist and business magnate. As the founder of the Ford Motor Company, he is credited as a pioneer in making automob ...

had an inline-five engine developed in the late 1930s to early 1940s for a compact economy car design, which never saw production due to lack of demand for small cars in the United States. The first production straight-five petrol engine was the Audi 2.1 R5 introduced in the Audi 100 in 1977. Audi has continued use of straight-five petrol engines (in both

naturally aspirated A naturally aspirated engine, also known as a normally aspirated engine, and abbreviated to N/A or NA, is an internal combustion engine in which air intake depends solely on atmospheric pressure and does not have forced induction through a turboc ...

and

versions) to the present day. The Audi TT RS and Audi RS3 currently use straight-five engines. In motorsport, the first car to use a straight-five engine was the

Audi Quattro The Audi Quattro is a road and rally car, produced by the German automobile manufacturer Audi, part of the Volkswagen Group. It was first shown at the 1980 Geneva Motor Show on 3 March. Production continued through 1991. Background The wor ...

rally car; other racing cars which used straight-five engines include the 1985-1986 Audi Sport Quattro E2 and the 1989 Audi 90 Quattro IMSA GTO. For the year 1987 factory team tested a 735 kW (1000 hp) version of the inline-5 powered Audi S1 Sport Quattro. Several Volkswagen-branded straight-five engines have been produced, beginning with the Volkswagen WH/WN 1.9 litre 10v engine used in the 1981 Volkswagen Passat. The final Volkswagen straight-five petrol engine was the Volkswagen EA855 2.5 litre 20v engine used in the North American Passat models until 2014. The Volvo Modular engine was introduced in the 1991 Volvo 850 sedan and was used in various Volvo models, along with the ''Ford Focus ST'' and ''Ford Focus RS'' models. All of the straight-five petrol engines used by Volvo and Ford were built at the Volvo Skövde engine plant in

Skövde Skövde () is a Urban areas in Sweden, locality and urban centre in Skövde Municipality and Västra Götaland County, in the Västergötland, Västergötland (Western Gothland region) in central southern Sweden. Skövde is situated around 150 k ...

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

, until their discontinuation in 2016. Other straight-five petrol engines include * 1989-1998 Honda G-series 2.0-2.5 litre 20v engines * 1995-2006 Fiat Family C 2.0-2.4 litre 20v engine * 2004-2012 General Motors Vortec 3500/ 3700 3.5-3.7 litre 20v engines In recent years the engine has been falling out of favour, with Volvo announcing in 2012 it would discontinue building them, for example.

Usage in motorcycles

Very few motorcycles have used five-cylinder engines. However, the 1965 ''Honda RC148'' and 1966 ''Honda RC149'' 125 cc four-stroke racing motorcycles used straight-five engines based on the 50 cc straight-twin engine from the Honda RC116 Grand Prix racing motorcycle. These straight-five engines were an unusual design in that they were configured as a straight-six engine with one of the middle cylinders removed.

References

{{Piston engine configurations Straight-05 5