The joy of six
The straight-six engine has been part of motoring life for well over a century.
The layout might have been even more common but for the fact that straight-sixes are longer than V8s of the same capacity, and correspondingly more difficult to package.
On the plus side, they have only one bank of cylinders and are therefore fairly simple technically.
They are also famously smooth and well-balanced when running. Even better, they sound glorious. Which classic car enthusiast has not at some time been inspired by the wonderful howl of a straight-six? Let’s enjoy 25 of the best.
1. Spyker 60hp
The first straight-six engine is believed to be the one built by Dutch brothers Jacobus and Hendrik-Jan Spijker for their 60hp racing car of 1903. This extraordinary machine’s other highlights included four-wheel brakes and an extremely early application of four-wheel drive.
The car was designed to compete in the disastrous 1903 Paris-Madrid race, in which several people died. Perhaps fortunately, the Spyker wasn’t ready in time.
British company Napier was close behind Spyker, producing a straight-six of its own in 1904.
2. Rolls-Royce Silver Ghost
‘Silver Ghost’ was originally the name of a particular Rolls-Royce 40/50hp, registered AX 201, though it has become common practice to use it for all examples of that model.
First shown in 1906, the Silver Ghost was only ever offered with a straight-six engine whose capacity started at 7.0 litres and was later extended to 7.4 litres.
The engine was very quiet for its time, and AX 201 was found to be almost completely reliable in thousands of miles of testing.
3. Renault 40CV
One of the many luxury cars for which Renault was known before the Second World War, the 40CV was produced from 1911 until 1928, first with a 7.5-litre straight-six engine and later with one measuring 9.1 litres.
Although designed to be elegant and refined, the 40CV was also so fast and reliable that it won the Monte-Carlo Rally in 1925.
The following year, a single-seater version set a new 24-hour world speed record, averaging 108mph.
4. AMC
American Motors Corporation fitted its new straight-six to the sporty Typhoon variant of the Rambler Classic in 1964. AMC was acquired 22 years later by Chrysler, which was happy to continue developing what was by now a rather old engine.
Described as being ‘as reliable as a block of wood’, the AMC straight-six survived until as late as 2006, 42 years after its first appearance. Among many other vehicles, it was used in 4.0-litre form in the second-generation Jeep Cherokee (pictured).
5. Aston Martin
Tadek Marek’s straight-six replaced an earlier engine of the same layout designed by WO Bentley for Lagonda.
The Marek ‘six’ made its debut in the DBR2 race car, and was then used in the DB4, the DB5 (famous for its appearances in James Bond movies), the DB6 and the DBS.
Ranging in size from 3.7 to 4.2 litres, the ‘six’ was eventually replaced by a V8, also designed by Marek.
6. Austin-Healey 3000
The Big Healey’s 2.9-litre straight-six engine was the most powerful variant of the BMC C-series.
This unit was designed by Morris and made its debut in 1954, five years before the Healey 3000 was introduced. It was fitted to several BMC saloons, including some versions of the Austin Westminster.
The Healey was the only car powered by a C-series to find success in international motorsport, performing superbly in top-level racing and rallying.
7. BMC E-series
The E-series was available both as a four-cylinder engine of either 1.5 or 1.7 litres, and as a straight-six of 2.2 or 2.6 litres.
The ‘six’ appeared in several vehicles built and sold in Australia and South Africa, and also in the UK-market Austin 1800 and later Princess (pictured), and identical models marketed with different badges.
The Princess was succeeded by the Ambassador, which was powered only by the later O-series four-cylinder engine.
8. BMW M1 and M5
BMW already had a long history of manufacturing straight-six engines when the dohc M88 unit arrived in 1978. It made its debut in the M1, the first of only two mid-engined production models BMW has ever produced (the other being the i8 hybrid).
The M88 also powered the first-generation M5, whose dramatic performance contrasted with its subdued appearance. A turbo version was used for Group 5 racing cars, while other derivatives appeared in the 6 Series coupé and 7 Series luxury saloon.
9. BMW M3 CSL
The CSL was a very fast, very expensive and very limited-production version of the third-generation (E46) M3.
Its 3.2-litre straight-six engine was familiar enough, appearing in other M3s of that era as well as high-performance variants of the Z3 and Z4 sports cars.
For the CSL, however, BMW upgraded the engine with revised camshafts and straighter inlet and exhaust manifolds. The power output went up from around 340bhp (depending on model) to nearer 360bhp.
10. Bristol
For its first luxury car, the 1947 400, the Bristol Aeroplane Company created a modified version of the 1971cc BMW M328 straight-six introduced in 1936. This was in turn the high-performance variant of the 1933 M78, the first in a long line of BMW straight-sixes.
Bristol continued to use this engine (latterly enlarged to 2.2 litres) before switching to Chrysler V8 power in 1961.
The company also supplied the unit to Frazer Nash and AC for their road cars, and to Cooper for its 1952 Formula Two racer.
11. Chevrolet Stovebolt
Chevrolet got into the straight-six game in 1929, when it introduced a new engine marketed as ‘a six for the price of a four’.
It gained the nickname ‘Stovebolt’ because its cylinder head bolts resembled those used on cast-iron wood-burning stoves.
Later Chevrolet ‘sixes’ are also sometimes referred to as Stovebolts, but properly speaking the original engine remained in production only until 1937, when it was replaced by a redesigned unit often known as the Blue Flame.
12. Chrysler Slant-Six
The Chrysler Slant-Six was unusual – though not unique – among straight-sixes in that the cylinders were inclined by 30 degrees from the vertical.
Unlike the BMC Mini in every other respect, it shared with the little British car a production run from 1959 to 2000.
The engine was used in a very wide variety of Chrysler models, including the Dodge Polara (pictured).
13. Datsun 240Z
The gorgeous Datsun 240Z (also known as the Nissan S30 and Nissan Fairlady Z) was powered by one of many engines from the L Series family, which included inline ‘fours’ as well as straight-sixes.
Only ‘sixes’ were used for the 240Z, with capacities of either 2.0 or 2.4 litres. A different 2.0-litre straight-six called the S20 was also used for some examples, but the L Series was far more common.
Larger versions were used for the later 260Z and 280ZX.
14. Ford Zephyr and Zodiac
The Ford Zephyr engine was manufactured in four- and six-cylinder forms. The straight-six powered models called Zephyr or Zodiac across several generations from 1954 to 1966, before being replaced by the more modern Essex V6.
The Zephyr ‘six’ was also used by smaller British manufacturers, including AC, Allard, Fairthorpe, Reliant and – extremely briefly – Lea-Francis.
15. Jaguar XK
The Jaguar XK straight-six made its debut in the XK120, which was unveiled in 1948 but did not go into full-scale production until 1950.
Jaguar used no other engine in its saloons, sports cars and competition vehicles until it introduced its new V12 in 1971.
However, the V12 did not replace the XK. The last production vehicle to use it was the Daimler DS420 limousine, which survived until 1992. Jaguar has since revived the XK to power its Lightweight E-type, XKSS, D-type and C-type ‘continuation models’.
16. Jaguar AJ6
Introduced in 1984, the AJ6 was only Jaguar’s third engine after the XK and the V12. It was another example of a slant-six, being inclined by 22 degrees from the vertical, and had an aluminium cylinder block. Jaguar produced versions with single- or double-overhead camshafts.
The AJ6 was first used in the 1983 XJ-S. Supercharged versions powered Jaguar’s first XJR model and the Aston Martin DB7. It was replaced in 1996 by the AJ-V8.
17. Maserati 3500GT
Maserati had enormous success – up to Formula One World Championship level – with its straight-six A6 engine.
When the company decided to spend more time building road cars, it adapted a 3.5-litre ‘six’ from the 350S sports racer and fitted it to the 3500GT (pictured).
Gradually increasing in size to 4.0 litres, the new engine was used in the 3500GT and its successor, the Sebring, from 1958 to 1969.
18. Mercedes-Benz 300SL
The dramatic gullwing-doored Mercedes-Benz 300SL, produced in first coupé and then roadster form from 1954 to 1963, was fitted with a straight-six based on an engine originally developed for the 300 Adenauer luxury saloon.
In the 300SL, the M198 unit was canted over by 50 degrees so that it would fit under the car’s low bonnet. It also featured dry-sump lubrication and direct fuel injection, both astonishing things to find in a road car of the period.
19. Mercedes-Benz C36 AMG
Launched in 1993, this was the first production car developed jointly by Mercedes-Benz and AMG after the former bought the latter in 1990. Its engine was the M104 straight-six used in many Mercedes models throughout the 1990s, and in SsangYongs into the 21st century.
AMG increased the capacity from the original 2.8 litres to 3.6. Along with other modifications, this raised the power significantly. The actual figure varied from one car to another, but it was always in the region of 280bhp.
20. Nissan Skyline GT-R R32
The third-generation Skyline GT-R, produced from 1989 to 1994, used a straight-six engine from Nissan’s extensive RB family.
In this application it measured 2.6 litres (about halfway through the RB’s range of 2.0 to 3.0 litres) and had two turbochargers.
The engine was officially rated at 276bhp, precisely the maximum allowed by the ‘gentleman’s agreement’ among Japanese manufacturers. Suspicions abounded that the actual output might have been a touch higher.
21. Rolls-Royce and Bentley
The last straight-six Rolls-Royce engine made its debut in the Silver Wraith and Bentley MkVI in 1946.
Both manufacturers continued to use it – for example in the Silver Dawn (pictured) – until the celebrated L-Series V8 made its debut in 1959.
The memorably smooth and quiet ‘six’ is often referred to as a B60. However, it has been pointed out that the Rolls-Royce B-Series engine family was designed for military and commercial use, and that the car engines are only superficially similar, with almost no interchangeable parts.
22. Toyota 2000GT
The Toyota M engine was a straight-six produced in many forms and fitted to larger Toyota models for nearly three decades.
The 3M version installed in the Toyota 2000GT sports coupé had considerable input from Yamaha.
Without forced induction, it produced 150bhp from 2.0 litres – a very impressive specific output even for a high-performance car of the late 1960s.
23. Toyota Supra Mk4
Like the M engine family mentioned previously, the Toyota JZ was a straight-six produced in various sizes. The most powerful version was the 3.0-litre twin-turbo fitted to the fourth-generation Supra.
In Japan it was rated at 280bhp, but for export markets the output was increased to 320bhp.
Every generation of Supra has had a straight-six engine, though the one in the current model is supplied by BMW. This is also the only Supra available with an alternative four-cylinder engine, also from BMW.
24. Triumph
The straight-six Triumph engine was based on a four-cylinder Standard unit, and made its debut in the Standard Vanguard in 1960.
Triumph first used it in the Vitesse saloon two years later, and subsequently in the Triumph 2000 and the GT6 coupé.
The ‘six’ also powered the TR5 (pictured) and TR6 sports cars. Previous TR models had been fitted with four-cylinder engines, a layout Triumph would return to with the TR7.
25. TVR Speed Six
Despite its reputation for producing cars with large V8 engines, TVR developed a straight-six which was used to power several of its models in the early 21st century, including the Cerbera, the Sagaris (pictured) and the extremely rare Typhon.
The Speed Six, as it was known, was also the basis for the fearsomely powerful Speed Twelve, which was used for a race version of the Cerbera and an aborted road car project.
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