View source for Straight-six engine

{{Short description|Internal combustion engine}}
{{Use dmy dates|date=October 2020}}

[[File:M20B25 block.jpg|thumb|right|Engine block of a [[BMW M20#M20B25|BMW M20]] straight-six engine (top view with cylinder head removed)]]

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 balance]], resulting in fewer vibrations than other designs of six or fewer cylinders.

Until the mid-20th century, the straight-six layout was the most common design for engines with six cylinders. However, [[V6 engine]]s gradually became more common in the 1970s and by the 2000s, V6 engines had replaced straight-six engines in most light automotive applications.

Due to their high and smooth torque, simplicity and reliability, weight and space, and balanced power delivery, straight-six engines are a common power source for [[truck]]s and [[bus]]es.

== Characteristics ==
In terms of packaging, straight-six engines are almost always narrower than a [[V6 engine]] or [[V8 engine]], but longer than [[straight-four engine]]s, V6s, and most V8s.<ref>{{cite web |title=V6 Vs Straight-Six: The Pros And Cons |url= https://www.carthrottle.com/post/v6-vs-straight-six-the-pros-and-cons/ |website=Car Throttle |access-date=12 September 2022}}</ref><ref>{{cite web |title=Everything you need to know about inline-six engines |url= https://www.whichcar.com.au/car-advice/inline-6-versus-v6-why-are-straight-sixes-making-a-comeback |website=WhichCar |access-date=12 September 2022}}</ref><ref>{{cite web |title=The 9 best straight-six engines |url= https://www.hagerty.com/media/archived/best-inline-six-engines/ |work=Hagerty |access-date=12 September 2022 |date=2 January 2018}}</ref> Compared to V-configuration engines with similar power and displacement, the straight configuration has fewer injectors, a single head, and a single exhaust manifold, all contributing to better reliability and performance.

Straight-six engines are typically produced in [[engine displacement|displacements]] ranging from {{convert|2|to|4|L|cuin|0|abbr=on}},<ref name="Cheetham">{{cite book|last=Cheetham|first=Craig|title=Ultimate American Cars|publisher=MotorBooks/MBI|year= 2006|url= https://books.google.com/books?id=y6DUvUpGmn0C&q=largest+six-cylinder+engine+automobile&pg=PA209 |isbn=978-0-7603-2570-4|access-date= 2012-10-11}}</ref>{{refpage|p209}} however engines range in size from the {{convert|0.7|L|cuin|0|abbr=on}} [[Benelli 750 Sei]] motorcycle engine<ref>{{cite web|last=Siegal |first=Margie |title=The Benelli Sei 750 |publisher=Motorcycle Classics |url= https://www.motorcycleclassics.com/classic-italian-motorcycles/benelli-sei-750/?PageId=1#axzz3MI6weXK5 |date=11 July 2007 |access-date=26 May 2024}}</ref> to the {{convert|10972.2|L|cuin|0|abbr=on}} [[Wärtsilä-Sulzer RTA96-C]] two-stroke marine diesel engine.  Due to its well-balanced configuration, the straight-six can be scaled up to substantial sizes for heavy trucks, locomotives, industrial and marine use.<ref name="Nunney"/>{{refpage|p4}}. When two straight-six engines are mated with a common crankshaft it forms a [[V12 engine]].

=== Engine balance and vibration ===
[[File:Inline 6 Cylinder with firing order 1-5-3-6-2-4.gif|thumb|Typical firing order of 1-5-3-6-2-4]]
[[File:marinestraight6.jpg|thumb|upright|right|3890-litre ''MAN B&W 6S60MC'' marine diesel engine]]

If an appropriate [[firing order]] is used, a straight-six engine has perfect primary and secondary [[engine balance]]. The primary balance is due to the front and rear trio of cylinders moving in pairs (albeit 360° out of phase), thus canceling out the rocking motion present in a [[straight-three engine]]. The secondary balance is due to the [[crank throw]]s being arranged in three planes offset at 120°, resulting in the non-sinusoidal forces summing to zero for all free forces until the sixth order.

The engine balance characteristics of a straight-six engine compare favorably with the more common [[straight-four engine]]s, [[V6 engine]]s, and [[V8 engine]]s which experience significant secondary dynamic imbalance, resulting in engine vibration.<ref name="Nunney">{{cite book|last=Nunney|first=M J|title=Light and Heavy Vehicle Technology |edition=Fourth |publisher=Butterworth-Heinemann |year=2006 |isbn=0-7506-8037-7}}</ref>{{refpage|pp12-13}} As engine reciprocating forces increase with the cube of piston bore, the straight-six is a preferred configuration for large truck and industrial engines.<ref name="Nunney"/>{{refpage|pp40-47}}

=== Two-stroke engines ===
An even-firing six-cylinder [[two-stroke]] engine requires ignitions at 60° intervals, or else it would run with simultaneous ignitions and be no smoother than a [[straight three engine|triple]] in power delivery. As such, it also requires crank throws at 60°{{Snd}}. Such designs appear to have been limited to diesel engines such as the Detroit [[Detroit Diesel Series 71|71 series]], marine engines, and outboard motors.

Some of the 120 possible crankshaft configurations have useful properties. Still, all of them have a rocking imbalance that may or may not require a balance shaft, depending on the application. The six pistons with six unique phases cannot be "paired" as in the four-stroke case. The Detroit engines used a configuration that, once the primary [[rocking couple]] was balanced out, was also perfectly balanced at all other rocking couples until the 6th order.<ref>{{cite web|url= http://dieselpro.com/detroit-diesel-crankshafts/671-crankshafts/detroit-diesel-r-5107033-crankshaft-671-standard-rebuilt.html#.Vntg9epsghU |title=Crankshaft For Detroit Diesel 6-71{{Snd}} DP R5 107033{{Snd}} |website=dieselpro.com}}</ref> [[Mercury Marine|Mercury]] came to use a configuration that canceled only the primary rocking couple and was run without a balancer.<ref>{{cite web|url= https://forums.iboats.com/forum/engine-repair-and-maintenance/mercury-mariner-outboards/394245-reed-valves|title=Reed valves Page: 1{{Snd}} iboats Boating Forums{{Snd}} 394245 |website=forums.iboats.com}}</ref>

The reciprocating masses of all configurations are still imbalanced at only 6th-order and up in their plane of motion. Still, the balance of kinetic energy exchange between pistons has improved to a residual 6th-order-and-up inertial torque oscillation compared with the four-stroke design being imbalanced at 3rd-order and up.

=== Crankshaft ===
[[File:I6crankandblock.jpg|thumb|Crankshaft with four main bearings]]
[[Crankshaft]]s for straight-six engines usually have either four [[main bearing]]s (i.e., a bearing in between each pair of [[crankpin]]s and one at each end) or seven main bearings (i.e., a bearing between every crankpin):
* Large displacement and diesel engines typically use seven bearings to minimize crankshaft flex. When an engine is subject to high loads at low speeds, the greater distance between main bearings causes increased crankshaft flex. Modern high-compression engines subject the crankshaft to greater bending loads from higher peak gas pressures, requiring the crank throws to have more significant support from adjacent bearings. So, it is common for straight-six engines to use seven main bearings.<ref name="Nunney"/>{{refpage|p38}}
* Smaller and high-performance engines{{when|date=September 2022}} typically use four bearings since having fewer main journals decreases friction and increases the torsional stiffness of the crankshaft. The lack of torsional stiffness can make the seven main bearing designs susceptible to torsional flex and potential breakage at high engine speeds. Any torsional flex in the crankshaft is compounded by the torsional flex of the [[camshaft]]s for the rear cylinders since the camshafts are rather long and subject to torsional flex. At high engine speeds, the combination of camshaft and crankshaft flex results in inaccurate timing of the valve openings, which, in the worst case, can cause the valves and pistons to collide with catastrophic results.

== Usage in cars ==
The first production straight-six engine was introduced in the [[Netherlands|Dutch]] ''[[Spyker]] 60 HP'' racing car in 1903.<ref>{{cite book |last1=Henry |first1=Alan |title=The 4-wheel Drivers: Racing's Formula for Failure? |date=1975 |publisher=Macmillan |isbn=978-0-333-17289-6 |url= https://books.google.com/books?id=k7D3PAAACAAJ |access-date=4 October 2022 |language=en}}</ref> Straight-six engines increased in popularity in the years after and by 1909, approximately 80 manufacturers were using them (including 62 in the United Kingdom).<ref name="Georgano">{{cite book|last=Georgano |first=G.N. |title=Cars: Early and Vintage, 1886–1930 |publisher=Grange-Universal |year=1985}}</ref> Prior to the 1950s, [[V6 engine]]s were rarely used, due to the poorer [[engine balance]] of V6 engines compared to straight-six engines. Since the 1980s, however, the shorter length of V6 engines has seen most manufacturers replace straight-six engines with V6 engines. An exception to this trend is the German brand [[BMW]], which has always used a straight-six layout for its six-cylinder engines.<ref>{{cite web|url= https://www.roadandtrack.com/car-culture/car-design/a30905623/inline-sixes-good/ |title=Why Inline-Six Engines Are Timeless |first=Kyle |last=Kinard |date=18 May 2020 |work=Road and Track |access-date=26 May 2024}}</ref>

Since 2017, the trend of switching to V6 engines has reversed due to the ability to create a modular engine family of straight engines sharing many components.<ref>{{cite web |url= http://blog.caranddriver.com/why-0-5-liter-cylinders-will-soon-dominate-automotive-engine-design/ |title=Why 0.5-Liter Cylinders Will Soon Dominate Automotive-Engine Design |last=Sherman |first=Don |publisher=Hearst Communications, Inc |date=27 January 2015 |access-date= 2016-11-01}}</ref><ref name="CarsGuide.com">{{cite web |title=Resurgence of the inline six-cylinder engine: Why Toyota Supra, BMW M3, Genesis GV80 and many others are choosing the straight-six |url= https://www.carsguide.com.au/car-news/resurgence-of-the-inline-six-cylinder-engine-why-toyota-supra-bmw-m3-genesis-gv80-and-many |website=CarsGuide.com |access-date=7 October 2022}}</ref> Examples include the 2017–present [[Mercedes-Benz M256 engine]], the 2019–present [[Ingenium engine family|Jaguar Land Rover Ingenium engines]] (AJ300 and AJ300D versions), the 2021–present [[Stellantis Hurricane engine]] and the 2022–present Mazda [[Skyactiv#Skyactiv-X|Skyactiv-X]] and [[Skyactiv#Skyactiv-D|Skyactiv-D]] engines.<ref>{{cite news|url= http://www.carmagazine.co.uk/car-news/tech/the-48-volt-future-of-the-mercedes-benz-four-and-straight-six-cylinder-engine/ |title=Straight sixes are back! Mercedes-Benz's new 48-volt engine family is here |last=Burt |first=Matt |date=28 October 2016 |access-date=11 November 2017}}</ref><ref name="CarsGuide.com"/><ref>{{cite web |title=V6 Vs Straight-Six: The Pros And Cons |url= https://www.carthrottle.com/post/v6-vs-straight-six-the-pros-and-cons/ |website=CarThrottle.com |access-date=7 October 2022 |language=en}}</ref>

=== Europe ===
[[File:BMW M1 Ausstellungsmotor.jpg|thumb|1978–1981 [[BMW M88]] engine]]
[[File:Volvo S60 Polestar - T6 3.0l V6 turbo (MSP16).jpg|thumb|2014–2016 [[Volvo SI6 engine|Volvo SI6]] engine (transversely mounted)]]

Alfa Romeo's first production straight-six engine – 6.3&nbsp;L [[flathead engine|flathead]] petrol engine – was introduced in 1921 in the [[Alfa Romeo G1]] luxury car. An [[overhead valve engine|overhead valve]] design was introduced in the 1922 [[Alfa Romeo RL]] sports car, and an [[overhead camshaft engine|overhead camshaft]] design was used in the 1927 [[Alfa Romeo 6C]] sports car and various racing cars from 1927 until 1954. The last Alfa Romeo model using a straight-six was the 1961–1969 [[Alfa Romeo 2600]] executive car before the company switched to V6 engines.

Mercedes-Benz's history of straight-six engines began with the 1913 [[Mercedes D.I]] aircraft engine. The first automotive straight-six engine was the 1924–1929 ''Daimler M836'' 3.9&nbsp;L petrol engine.<ref>{{cite web |title=The Origin of the Mercedes 'W' Chassis Designation |url= https://www.thedrive.com/news/18783/the-origin-of-the-mercedes-w-chassis-designation |website=thedrive.com |date=27 February 2018 |access-date=27 December 2020}}</ref> Following World War 2, Mercedes resumed production of straight-six engines with the 1951 introduction of the [[Mercedes-Benz M180 engine|Mercedes-Benz M180]] overhead camshaft engine. In 1985, the [[Mercedes-Benz OM603]] 3.0&nbsp;L diesel straight-six engine was introduced. In 1996, the company replaced its petrol straight-sixes with a series of V6 engines, although it continued producing diesel straight-six engines. Production of petrol straight-six engines resumed in 2017 with the introduction of the [[Mercedes-Benz M256 engine|Mercedes-Benz M256]] turbocharged DOHC engine.

Opel began production of straight-six engines in 1927 with a 1.8&nbsp;L flathead petrol engine used by the [[Opel 8/40 PS]]. The displacement of this engine was expanded as it was used in later models such as the [[Opel Kapitän]] and [[Opel Admiral]], with later versions switching to an overhead valve (pushrod) design. In 1968, the straight-six versions of the [[Opel cam-in-head engine#Six-cylinder versions|Opel CIH engine]] were introduced, initially using a single overhead camshaft (SOHC) with some later versions using double overhead camshafts (DOHC). Production of the Opel CIH engine continued until 1993, when a V6 engine replaced it.

Volvo began production of straight-six engines with the 1929–1958 [[Penta DB]] flathead petrol engines. The company resumed production in 1969 with the [[Volvo B30 engine|Volvo B30]] overhead valve petrol engine, followed by the straight-six versions of the [[Volvo Modular engine#B6254FS|Volvo Modular Engine]] introduced in 1995 and then the [[Volvo SI6 engine]] introduced in 2006. Several models (such as the 1998–2006 [[Volvo S80#First generation (1998–2006)|Volvo S80]]) used the uncommon design of a transversely-mounted straight-six engine. Production of Volvo straight-six engines ceased in 2015.

BMW's first product was the 1917 [[BMW IIIa]] straight-six aircraft engine. The company began production of automotive straight-six engines in 1933 with the [[BMW M78]] petrol engine, a 1.2&nbsp;L overhead valve design that evolved over the years into the [[BMW M337]] (produced until 1958). Production of straight-six engines resumed in 1968 with the [[BMW M30]] single overhead camshaft engine, built for 27 years and used in various models. The 1978–1989 [[BMW M88]] engine was a double overhead camshaft design that was introduced in the [[BMW M1]] mid-engine sport car. BMW's introduction of turbocharged straight-six engines (aside from the low-volume variants of the M30 engine in the 1980s) was in 2006 [[BMW N54]] and the production of naturally aspirated engines ceased in 2015. {{as of|2022}}, the [[BMW B58]] turbocharged straight-six engine remains in production,<ref>{{cite web|last1=Murphy|first1=Tom|title=Seven Turbos, Three Hybrids Share Wards 10 Best Engines Honors 2017 &#124; Wards 10 Best Engines|url=http://wardsauto.com/2017/seven-turbos-three-hybrids-share-wards-10-best-engines-honors|website=WardsAuto|publisher=Penton|access-date=24 May 2017|date=12 December 2016}}</ref> along with its higher performance [[BMW S58]] variants.

=== United Kingdom ===
{{multiple image
 | align     = right
 | direction = vertical
 | width     = 200
 | image1    = RR40 50SG.jpg
 | alt1      = Colored dice with white background
 | caption1  = [[Rolls-Royce Silver Ghost]] flathead engine
 | image2    = 1969 Jaguar XJ6 engine.JPG
 | caption2  = 1969 [[Jaguar XK engine|Jaguar XK]] [[Overhead camshaft engine#Double overhead camshaft (DOHC)|DOHC]] engine
}}

Rolls-Royce's first straight-six engine was a 6.0&nbsp;L [[IOE engine|IOE]] petrol engine, which was used in the 1905 [[Rolls-Royce 30 hp]] luxury car. This car was replaced by the 1906–1926 [[Rolls-Royce Silver Ghost]], which switched to a flathead (side-valve) design for its straight-six engine.

In 1906, the ''[[Standard Motor Company|Standard]] Six'' luxury car was introduced, powered by a {{convert|20|hp|kW PS|0|abbr=on}} I6 petrol engine.<ref>{{cite web |title=Standard |url= https://www.ukcar.com/history/Standard/index.html |website=ukcar.com |access-date=8 October 2022}}</ref> Standard's engines were also used in several cars built by SS Cars and its successor Jaguar, such as the 1932 [[SS 1]] sports car, the 1936 [[SS Jaguar 100]] and the 1938 [[Jaguar Mark IV#SS Jaguar and Jaguar 3½ Litre|Jaguar 3½ Litre]] sports saloon/coupe and the 1948 [[Jaguar Mark V]] luxury car.

The 1927 [[Rover Two-litre]] luxury car introduced the company's [[IOE engine|IOE]] straight-six petrol engine. This engine was used in various Rover models until the [[Rover P5]] was discontinued in 1973, and in various Land Rover models from the 1961 [[Land Rover series#Series IIA|Land Rover Series IIA]] until 1980{{citation needed|date=October 2022}} [[Land Rover series#Series III|Land Rover Series III]].

The 1928 [[Austin Twenty#20/6 Six-cylinder engine|Austin 20/6]] luxury car introduced Austin's flathead straight-six petrol engine. The 1938–1939 Austin Twenty-Eight used an enlarged version of this engine. This was replaced by the [[Austin D-Series engine]], an overhead valve engine initially designed for trucks, which was used in passenger cars from 1947 until 1968 (along with several [[Jensen Motors]] models from 1946 to 1962). The overhead valve [[BMC C-Series engine|BMC C-Series]] was used by various BMC brands from 1954 to 1971, followed by the 2.2&nbsp;L version of the [[BMC E-series engine#2.2-litre engines|BMC E-Series]] overhead camshaft engine, which was produced from 1970 until 1982.<ref>{{cite book |last=Daniels |first=Jeff |date=1980 |title=British Leyland, the truth about the cars |publisher=Osprey |isbn=9780850453928}}</ref>

The 1930–1936 [[Wolseley Hornet six]] lightweight car was powered by a 1.3–1.6&nbsp;L overhead camshaft straight-six petrol engine.

The 1931–1932 [[MG F-type]] tourers, 1932–1934 [[MG K-type]] sports cars, and 1934–1936 [[MG N-type]] sports cars were powered by an overhead camshaft straight-six petrol engine.

During the mid-1930s, the [[Riley MPH]] sports car and ''Riley Kestrel 6''<ref>{{cite web |title=1934 Riley Kestrel 6 Cylinder S/S |url= https://ashridgeautomobiles.co.uk/sales/1934-riley-kestrel-6-cylinder-s-s/ |website=Ashridge Automobiles |access-date=9 October 2022}}</ref> saloon were produced in small numbers and were powered by dual overhead camshaft straight-six petrol engine.

The 1947 [[Bristol 400]] luxury car was powered by an overhead valve straight-six petrol engine based on the design of the [[BMW M328]] engine. This engine remained in use until the [[Bristol 406]] was discontinued in 1961.

The dual overhead camshaft [[Jaguar XK6 engine]] petrol engine was produced from 1948 to 1992 in the [[Jaguar XK120]] sports car. Introduced as a 3.4&nbsp;L, it was used in passenger and racing cars, produced in displacements of 2.4 to 4.2&nbsp;L. The XK6 engine was followed by the [[Jaguar AJ6 engine|AJ6 and AJ16]] engines, produced from 1984 to 1996, before being replaced by a Ford-derived V6 engine.

The 1948–1959 [[Lagonda straight-6 engine|Lagonda straight-6]] dual overhead camshaft petrol engine was used in various Aston Martin and Lagonda cars. This engine's successor was the Tadek Marek-designed straight-six used in the DB4 (1958), DB5 (1963), DB6 (1965) and DBS (1967).

The [[Ford Zephyr engine#Zephyr 6|Ford Zephyr 6]] overhead valve engine was used in the ''Ford Zephyr'' executive car and several other models from 1951 to 1966.

The [[Triumph I6]] overhead valve straight-six petrol engine was produced from 1960 to 1977 and debuted in the Standard Vanguard Six sports saloon. The [[Leyland PE166 engine|Leyland PE166]] engine was loosely based on the Triumph design and was produced from 1977 to 1986.

The 1972–1977 [[TVR M series#2500M|TVR 2500M]] sports car was powered by the Triumph I6 engine. Then, from 1999 to 2007, TVR's own [[TVR Speed Six engine|TVR Speed Six]] dual overhead camshaft engine was used in several of the company's sports cars.

=== United States ===
{{multiple image
 | align     = right
 | direction = vertical
 | width     = 200
 | image1    = 1954HudsonWasp-engine.jpg
 | caption1  = 1954 [[Hudson Wasp]] engine
 | image2    = 1977 Gremlin white azen.jpg
 | caption2  = 1977 [[AMC straight-6 engine]]
}}

The 1906–1908 [[Ford Model K]] luxury car used a {{convert|405|cuin|L|1|abbr=on}} straight-six petrol engine and was the only Ford six-cylinder passenger car engine until the 1940s. The [[Ford straight-six engine#First generation|Ford flathead I6]] was produced from 1941 until 1951, followed by the [[Ford straight-six engine#Second generation|Ford OHV I6]] overhead valve engine from 1952 through 1964, then the [[Ford straight-six engine#Third generation|Ford Thriftpower Six]] overhead valve engine from 1960 until 1982, and the [[Ford straight-six engine#Fourth generation|Ford 240 I6]] from 1965 through 1972. The [[Ford straight-six engine#300|Ford {{convert|300|cuin|L|1|abbr=on}} version]] of the straight-six engine was built from 1965 until 1996, with notable uses in trucks, SUVs, and vans. However, Ford straight-sixes were replaced by V6 engines in passenger cars during the mid-1970s.

In 1908, the [[Oldsmobile Model Z]] was powered by a flathead straight-six petrol engine, which was produced until 1912 (in the [[Oldsmobile Limited]] luxury car) in displacements of {{convert|453|cuin|L|1|abbr=on}}, {{convert|505|cuin|L|1|abbr=on}} and {{convert|706|cuin|L|1|abbr=on}}. Oldsmobile's next straight-six engine was introduced in the 1913 [[Oldsmobile Six]] luxury car, initially with a displacement of {{convert|380|cuin|L|1|abbr=on}}, followed by a displacement of {{convert|177|cuin|L|1|abbr=on}} for the 1917–1921 [[Oldsmobile Six#Reintroduction|Oldsmobile Model 37]] luxury car. The later generations of the [[Oldsmobile straight-6 engine|Oldsmobile Straight-6]] also used a flathead design from its introduction in the 1923 [[Oldsmobile Model 30]] luxury car until it was replaced in 1950 by Oldsmobile's V8 engine.

The 1913–1929 [[Oakland Six]] luxury car was powered by a flathead petrol engine produced in displacements of {{convert|177|cuin|L|1|abbr=on}} and {{convert|334|cuin|L|1|abbr=on}}. In 1926, the [[Pontiac Six]] was introduced as a lower-cost version of the Oakland six, powered by the [[Pontiac straight-6 engine#"Split Head" Six|Pontiac Split-Head Six]] flathead engine, which used two cylinder heads. This engine was replaced by the 1941–1954 [[Pontiac straight-6 engine#Flathead Six|Pontiac flathead six]]. The unrelated [[Pontiac straight-6 engine#Overhead Valve|Pontiac OHV 6]] overhead valve engine was produced in 1964–1965, based on a Chevrolet design. Pontiac's final straight-six engine was the 1966–1969 [[Pontiac straight-6 engine#Overhead cam|Pontiac OHC 6]] overhead camshaft engine, which was replaced by Chevrolet's straight-six engine and Buick's V6 engine.

The overhead valve [[Buick Straight-6 engine|Buick Straight-6]] petrol engine was introduced in the 1914 [[Buick Six]] luxury car and was produced until 1930. Buick did not make another six-cylinder engine until they introduced a V6 engine in 1962.

The 1916 through 1926, [[Hudson Super Six]] was powered by a {{convert|289|cuin|L|1|abbr=on}} straight-six petrol engine. This was followed by an [[IOE engine|IOE]] version in 1916. The 1951 [[Hudson Hornet]] introduced a {{convert|308|cuin|L|1|abbr=on}} flathead straight-six engine.<ref>{{cite web|last=Roberts |first=Andrew |title=Classic Cars: The Hornet|work=The Independent|date=19 June 2007 |url= http://classified.independent.co.uk/cars/article2667213.ece |archive-url= https://web.archive.org/web/20090131095328/http://www.independent.co.uk/extras/cars/classic-cars-the-hornet-453564.html |archive-date=31 January 2009|url-status=dead |access-date=26 May 2024}}</ref> These engines dominated dirt track and NASCAR racing at the time.<ref>{{cite web|url= https://bangshift.com/general-news/tech-stories/look-at-the-hudson-308ci-inline-six/ |title=The Other 3/08: Here’s A Look At The Hudson 308ci Inline Six! |date=8 March 2023 |first=Brian |last=Lohnes |website=bangshift.com |access-date=26 May 2024}}</ref><ref>{{cite web|url= https://www.museumofamericanspeed.org/hudson.html |title=Hudson Twin H-Power 6 Cylinder |work=Museum of American Speed |date=2023 |access-date=26 May 2024}}</ref><ref>{{cite web|url= https://www.autoevolution.com/news/the-story-of-the-hudson-hornet-the-forgotten-six-cylinder-muscle-car-167773.html |title=The Story of the Hudson Hornet, the Forgotten Six-Cylinder Muscle Car |date=21 August 2021 |first=Ciprian |last=Flore |website=autoevolution.com |access-date=26 May 2024}}</ref> Production of the Hudson I6 continued after the 1954 merger forming [[American Motors Corporation]] and was eventually replaced by a new [[AMC V8 engine|Rambler V8]] after 1956.

In 1924, Chrysler began production of a straight six version of the [[Chrysler flathead engine|Chrysler flathead]] petrol engine. This was replaced by the 1959–2000 [[Chrysler Slant-6 engine|Chrysler Slant-6]] overhead valve straight-six petrol engine, which was so named due to the 30-degree angle used to reduce the height of the engine (with the trade-off of a wider engine). The Slant-6 was released in the [[Dodge Dart#First generation (1960–1961)|Dodge Dart]] economy car and used in many models until a V6 engine replaced it after 30 years.

The [[Chevrolet Stovebolt engine|Chevrolet Stovebolt]] overhead valve straight-six petrol engine was introduced in 1929 as a replacement for the brand's straight-four engines and was produced in displacements of {{convert|181|cuin|L|1|abbr=on}}, {{convert|194|cuin|L|1|abbr=on}} and {{convert|207|cuin|L|1|abbr=on}}. The second generation of this engine family – often referred to as the [[Chevrolet Stovebolt engine#Second generation: 1937–1962|Blue Flame]] engine – was produced from 1937 to 1962 in displacements of {{convert|216|cuin|L|1|abbr=on}}, {{convert|235|cuin|L|1|abbr=on}} and {{convert|261|cuin|L|1|abbr=on}}. This was followed by the 1962–1988 [[Chevrolet Turbo-Thrift engine]] (also using an overhead valve design), which was replaced by various General Motors V6 engines.

The 1952 through 2006, [[AMC straight-6 engine|AMC Straight-6]] petrol engine initially used a flathead design before being upgraded to an overhead valve design in 1956. A new I6 design with a short stroke and seven [[main bearing]] crankshaft was introduced in 1964.<ref>{{citation |first=David V. |last=Potter |first2=George F |last2=Leydorf, Jr. |first3=Robert L. |last3=Lawler |title=The new Rambler Six Engine - Torque Command 232 (Technical Paper 640276) |publisher=Society of Automotive Engineers |date=June 1964 |doi=10.4271/640276}}</ref> The engine was rugged, reliable, and became noted for longevity. A turbocharged racing engine based on the AMC Straight-6 engine block produced {{convert|875|hp|kW|0|abbr=on}} and competed in the 1978 Indianapolis 500 race.<ref>{{cite web|last=Wilson |first=Michael |title=When the Roar was Red, White & Blue: American Motors and the Indy 500 |url= http://geocities.com/mmbb444/page32.html |archive-url= https://web.archive.org/web/20091025232202/http://geocities.com/mmbb444/page32.html |archive-date=25 October 2009 |access-date=26 May 2024}}</ref><ref>{{cite web|url= https://www.hemmings.com/stories/article/barney-navarro |title= Barney Navarro - Unconventional thinking and hard work put his products in the record books |first=Daniel |last=Strohl |date=23 September 2018 |work=Hemmings |access-date=26 May 2024}}</ref> The final application for the AMC Straight-6 engine was the 2006 [[Jeep Wrangler (TJ)]], after which a V6 replaced it.<ref>{{cite web|url= https://www.motortrend.com/how-to/154-0604-jeeps-kick-ass-engine-history-4-liter/ |title=Jeeps Kick Ass Engine - The History Of The 4.0L |first=Tori |last=Tellem |date=1 April 2006 |work=Motor Trend |access-date=26 May 2024}}</ref>

The 1962 through 1973, [[Jeep Tornado engine|Jeep Tornado]] overhead camshaft straight-six engine was introduced in the [[Willys Jeep Station Wagon]].<ref>{{cite web |url= https://www.ifsja.org/tech/motors/tornado.html |last=Page |first=Ben |title=Tornado 230 CI Engine Information / History |publisher=International Full Size Jeep Association |year=2006 |access-date=26 May 2024}}</ref> At the time of its introduction, the Tornado engine had the lowest specific fuel consumption of an American gasoline (petrol) engine.<ref>{{cite magazine|url= http://www.4wdandsportutility.com/features/jeep/0801_4wd_1963_jeep_wagoneer/history.html |first=Patrick |last=Foster |title=1963 Jeep Wagoneer - Landmark Vehicle |magazine=4Wheel Drive & Sport Utility Magazine |date=January 2008 |url-status=dead |archiveurl= https://web.archive.org/web/20110722115240/http://www.4wdandsportutility.com/features/jeep/0801_4wd_1963_jeep_wagoneer/history.html |archivedate=22 July 2011 |access-date=26 May 2024}}</ref> The Tornado engine was replaced by the AMC I6 engine.

In 2001, General Motors resumed production of straight-six engines with the [[General Motors Atlas engine#LL8 (Vortec 4200)|Vortec 4200]] dual overhead camshaft petrol engine. This engine was used in various SUV models until 2009.<ref>''4200 Overview''</ref> Also, the [[Duramax I6 engine|Duramax Straight-6]] turbocharged diesel engine has been available in several General Motors SUV and light truck models since 2020.<ref>{{cite web |title=2019 Chevrolet Silverado Adds 3.0L Duramax Diesel, Ditches 450 lbs - GM Inside News |url= http://www.gminsidenews.com/articles/2019-chevrolet-silverado-adds-3-0l-duramax-diesel-ditches-450-lbs/ |website=GM Inside News |date=13 January 2018}}</ref>

On March 25, 2022, Stellantis announced their new twin-turbocharged straight-six engine, the [[Stellantis Hurricane engine]].<ref>{{cite press release |title=Stellantis Media - Stellantis Debuts Hurricane Twin-turbo I-6 Engine That Cuts Emissions, Increases Fuel Economy And Is More Powerful |url= https://media.stellantisnorthamerica.com/newsrelease.do?id=23660&mid= |access-date=2023-02-03 |website=media.stellantisnorthamerica.com}}</ref> The 3.0&nbsp;L Hurricane is produced at Stellantis’ [[Saltillo Engine Plant]] in Mexico. Two versions are available, based on power and torque output. The Standard Output (SO) at {{cvt|420|hp|kW PS|0}} and {{cvt|268|lb·ft|N·m|0}} of torque, and the High Output (HO) at variously at {{cvt|510-550|hp|kW PS|0}} and {{cvt|500-531|lb·ft|N·m|0}} of torque, depending on model and model year. The turbos on the SO variant deliver a peak boost of 22 psi, while the HO turbos deliver 26 psi of peak boost.

=== Asia ===
{{multiple image
 | align     = right
 | direction = vertical
 | width     = 200
 | image1    = Nissan S20 engine 001.JPG
 | caption1  = 1970s [[Nissan S20 engine]]
 | image2    = Nissan_RB26DETT_Engine_-_Front_Side.jpg
 | caption2  = 1990s [[Nissan RB engine]]
}}

Toyota's first straight-six engine was the [[Toyota Type A engine|Toyota Type A]], produced from 1935 through 1947. The Type A was an overhead-valve petrol engine based on the ''Chevrolet Stovebolt'' engine. This was followed by the first generation [[Toyota F engine#F|Toyota F]] overhead valve engine, which was produced from 1949 to 1975, which in turn was followed by the [[Toyota F engine#2F|2F version]] from 1975 to 1988 and the fuel-injected [[Toyota F engine#3F/3F-E|3F / 3FE version]] from 1988 to 1992. This was replaced by the dual overhead camshaft [[Toyota FZ engine]], produced from 1993 until 2008. Produced alongside these engines was the single overhead camshaft [[Toyota M engine]], which was introduced in 1965 and produced over seven generations until 1993 (with the ''7M-GTE'' being the final version of the M engine). The M engine was replaced by the dual overhead camshaft [[Toyota JZ engine]], arguably known as the company's best straight-six engine, which was produced from 1990 to 2007. Toyota's third line of straight-six engines was the 2.0&nbsp;L [[Toyota G engine]], which was released as a single overhead camshaft engine in 1979 and upgraded to dual overhead camshafts before production ended in 2008 (with the 1G-FE being the final variant).

Nissan's first straight-six engine was the 1950–1952 [[Nissan P engine#NAK|Nissan NAK]] flathead petrol engine, which continued in various forms until production of the [[Nissan P engine#P|Nissan P]] engine ended in 2003. The 1963–1965 [[Nissan H engine#K|Nissan K]] overhead valve petrol engine was used in the [[Nissan Cedric#Cedric Special 50|Nissan Cedric Special 50]] luxury car. Using a similar design, the [[Nissan H engine#H30|Nissan H30]] engine was used in several luxury cars from 1965 through 1989. In 1966, Nissan began production of the six-cylinder versions of the single overhead camshaft [[Nissan L engine]], which was used in the [[Nissan Fairlady Z|Datsun (Nissan) 240Z/260Z/280Z]] and other Nissan/Datsun cars, and was produced until 2009. The 1985–2004 [[Nissan RB engine]], used in the [[Nissan Skyline]] and several other cars, was produced in single overhead camshaft and dual overhead camshaft configurations until a V6 engine replaced it. The [[Nissan TB engine|Nissan TB]] overhead valve engine was introduced in 1987 and produced alongside the other straight-six engines.

The six-cylinder versions of the [[Prince G engine]] were introduced in 1963 and remained in production until 1969, three years after Prince's merger with Nissan. The 1969–1973 [[Nissan S20 engine|Nissan S20]] dual overhead camshaft engine (used in the [[Nissan S30#Fairlady Z432|Nissan Fairlady]] and first generation of the [[Nissan Skyline#GT-R|Nissan Skyline GT-R]]) was based on the Prince G engine.

Mitsubishi produced six-cylinder versions of the [[Mitsubishi KE engine]] from 1963 to 1970, as well as the rare six-cylinder versions of the [[Mitsubishi Saturn engine#6G34|Mitsubishi 6G34]] version of the single overhead camshaft "Saturn" engine from 1970 to 1976.

The 2000–2006 [[Daewoo Magnus]] (also called the Chevrolet Evanda, Chevrolet Epica, Holden Epica, or Suzuki Verona) was powered by the ''Daewoo XK6'' straight-six petrol engine, which is one of the few straight-six engines to be used in a [[transverse engine]] front-wheel drive car.

=== Australia ===
{{multiple image
 | align     = right
 | direction = vertical
 | width     = 200
 | image1    = Chrysler hemi 245.jpg
 | caption1  = 1970 [[Chrysler Hemi-6 Engine]]
 | image2    = Barra 270T.jpg
 | caption2  = 2004–2009 [[Ford Barra engine]]
}}
From the 1950s to the 2010s, many cars produced in Australia were powered by a straight-six engine.

Holden's first car, the 1948 [[Holden 48-215]] sedan, was powered by the [[Holden straight-six motor#Grey|Holden 'grey' motor]], an overhead valve petrol engine. This engine was replaced by the [[Holden straight-six motor#Red|Holden 'red' motor]], which was produced from 1963 to 1980 and in turn followed by the 1980–1984 [[Holden straight-six motor#Blue|Holden 'blue' motor]]. The final locally produced Holden straight-six was the 1984–1986 [[Holden straight-six motor#Black|Holden 'black' motor]], which was initially replaced by the Japanese-built [[Nissan RB engine#RB30|Nissan RB30]] engine before Holden switched to a locally-built V6 engine.

Ford produced straight-six engines for the longest time of any Australian manufacturer. In 1960, the [[Ford Falcon (Australia)|Ford Falcon]] large sedan was introduced with a locally-built version of the American [[Ford straight-six engine#Ford Australia|Ford Straight-6]] overhead valve engine. In 1998, these engines were upgraded to a single overhead camshaft design. This was followed in 2002 by the [[Ford Barra engine|Ford Barra]] dual overhead camshaft engine in 2002, which was produced in both naturally aspirated and turbocharged versions. The Ford Barra engine remained in use until Ford Australia ceased local production in 2016.

The [[Chrysler Valiant]] was introduced in 1962, powered by the American [[Chrysler Slant-6 engine|Chrysler Slant-6]]. In 1970, the Valiant switched to the [[Chrysler Hemi-6 Engine|Chrysler Hemi-6]] overhead valve engine, an Australia-only engine that was produced until Chrysler Australia ceased production of large cars in 1981.<ref>{{cite web |author=''Wheels'' staff |title=Australia's top 10 engines |url= https://www.whichcar.com.au/features/australias-top-10-engines |publisher=whichcar Australia |date=26 January 2017 |access-date=8 October 2019}}</ref>

The 1962–1965 [[Austin Freeway]] and [[Wolseley 24/80]] large sedans were powered by BMC Australia's ''Blue Streak'' overhead valve petrol engine. This was followed by the six-cylinder versions of the [[BMC E-series engine|BMC E-series]] overhead camshaft engines, which were introduced in the 1970 [[Austin Kimberley|Austin Kimberley / Austin Tasman]] front-wheel-drive sedans, which were produced until 1972.<ref>{{cite book |last=Davis |first=Tony |year=1987 |title=Aussie Cars |publisher=Marque Publishing |isbn=9780947079017 }}</ref> This engine was upsized to a 2.6&nbsp;L displacement in 1973 and used [[Leyland P76]] and the [[Morris Marina]] large cars until 1975.<ref>{{cite book|last=Robson |first=Graham |year=2000 |edition=2nd |title=The Cars of BMC |publisher=Motorbooks International |isbn=9781899870417 }}</ref>

== Usage in motorcycles ==
[[File:Honda CBX Engine Detail.jpg|thumb|1978–1982 [[Honda CBX]] engine]]

From 1964 to 1967, Honda produced several [[Grand Prix motorcycle racing]] motorcycles powered by straight-six versions of the [[Honda RC series|Honda RC]] petrol racing engine; these versions were designated the '3RC164', 'RC165', 'RC166' and [[Honda RC174]].<ref>''Honda's Race History''</ref> The unrelated road-use [[Honda CBX]] was produced from 1978 to 1982 and was powered by a {{convert|1047|cc|cuin|abbr=on|1}} dual overhead camshaft petrol engine.<ref>Honda CBX 1000 Gold Portfolio 1978–1982. R. M. Clarke. Brooklands Books, 24 January 1999</ref><ref>{{cite web|url= http://www.motorcycleclassics.com/motorcycle-reviews/1981-honda-cbx.aspx |title=1981 Honda CBX|publisher=Motorcycle Classics|access-date=11 November 2009 |date=November–December 2009 |first=Greg |last=Williams}}</ref>

The 1973–1989 [[Benelli Sei]] series was the first road-use motorcycle to use a straight-six engine. Initially released with a {{convert|747|cc|cuin|abbr=on|1}} single overhead camshaft petrol engine, in 1979 it was upgraded to a {{convert|906|cc|cuin|abbr=on|1}} engine.<ref>{{cite book |title=The Ultimate Motorcycle Book |first=Hugo |last=Wilson |publisher=Dorling Kindersley|date=1999 |isbn=9780751306538}}</ref>

The 1979–1989 [[Kawasaki Z1300]] roadster motorcycle was powered by a {{convert|1286|cc|cuin|abbr=on|1}} dual overhead camshaft petrol engine.<ref>{{cite book|title=Ultimate History of Fast Bikes |first=Roland |last=Brown |date=2004 |publisher=Parragon |isbn=9781405437325}}</ref>

From 2011–present, the [[BMW K1600]] series of touring motorcycles have been powered by a {{convert|1649|cc|cuin|abbr=on|1}} dual overhead camshaft petrol engine.<ref>{{cite web |url= http://www.motorcyclenews.com/MCN/News/newsresults/New-bikes/2010/june/jul0210-bmw-announce-k1600-gt-and-gtl/ |work=Motorcycle News |title=BMW announces K1600 GT and K1600 GTL six-cylinder tourers| first=Chris |last=Newbigging |date=2 July 2010| access-date=22 July 2010}}</ref><ref name=mcusa>{{cite web | url= http://www.motorcycle-usa.com/616/7370/Motorcycle-Article/2011-BMW-K1600GT-First-Look.aspx |title=2011 BMW K1600GT First Look |first=Bart |last=Madson |date=2 July 2010 |website=motorcycle-usa.com |access-date=22 July 2010}}</ref>

== Usage in trucks ==
Straight-six engines used in trucks include:
* 5.9 and 6.7&nbsp;L versions of the 1984–present [[Cummins B Series engine|Cummins B Series]] turbocharged diesel engine<ref>{{cite web |url= http://www.ramtrucks.com/en/towing_guide/ |title= Ram Trucks Towing & Payload Capacity |date= 2016 |publisher= Ram Trucks |access-date= 2016-11-17}}</ref>
* General Motors' 2002–2009 [[General Motors Atlas engine#LL8 (Vortec 4200)|Vortec 4200]] naturally-aspirated petrol engine

== Diesel engines ==
=== Automotive engines ===
Straight-six engines used in automobiles include:
* 1978–1995 [[Volkswagen D24 engine|Volkswagen D24]] naturally-aspirated engine and the 1982–1992 [[Volkswagen D24T engine|Volkswagen D24T]] turbocharged engine
* 1986–1997 [[Mercedes-Benz OM603]] engine – produced in naturally aspirated and turbocharged variants
* BMW's line of diesel engines consists of the [[BMW M21]] (introduced in 1981) through to the current [[BMW B57]] engine
* 1985–2009 [[Nissan RD engine|Nissan RD]] (naturally-aspirated and turbocharged variants) and 1987–2007 [[Nissan TD engine#TD42|Nissan TD42]] (turbocharged) engines
* [[General Motors]] offers the [[Duramax I6 engine]] for light duty pickup trucks.

=== Industrial-use and truck engines ===
* various [[List of Toyota engines#Straight-6 2|Toyota engines]] from 1956–present
* [[Caterpillar Inc.|Caterpillar]] manufactures several inline six-cylinder diesel engines, known for their reliability and use in various industrial and commercial applications. These engines include the C13, C7, 3126, and others, ranging in size and power output.
* [[Cummins B Series engine|Cummins B Series]] (5.9 and 6.7&nbsp;L versions) from 1984–present
* [[Detroit Diesel]] DD13 and DD15 used in [[Semi-trailer truck|semi-trailer trucks]].
* industrial and truck engines from [[International Motors|International]], [[MAN Truck & Bus]],<ref>{{cite web | url = https://www.engines.man.eu/global/en/index.html | title = MAN Engines | access-date = 2022-02-01}}</ref> [[Scania AB|Scania]]<ref>{{cite web | url = https://www.scania.com/group/en/section/solutions/ | title = Scania Solutions | access-date = 2016-09-08}}</ref> and [[China Yuchai International|Yuchai]]
* A [[V12 engine]] is a twelve-[[Cylinder (engine)|cylinder]] [[Internal combustion engine#Reciprocating engines|piston engine]] where two six cylinder banks are arranged in a [[V engine|V configuration]] around a common [[crankshaft]].

== See also ==
{{commons category|Straight-6 engines}}
* [[Flat-six engine]]
* [[V6 engine]]
* [[VR6 engine]]
* [[V12 engine]]
{{clear right}}

== References ==
{{reflist|30em}}

{{Piston engine configurations|state=expanded}}

{{DEFAULTSORT:Straight-Six Engine}}

[[Category:Piston engine configurations|Straight-06]]
[[Category:Straight-six engines| ]]
[[Category:Straight engines|6]]