Bentley Speed Six

Bentley 6½ Litre & Speed Six
Speed Six Mulliner drophead coupé 1930 original body, chassis LR2766, engine KR2698, registration GH 1517. First owner a Miss Bingham
Overview
Manufacturer	Bentley Motors Limited
Production	1926–1930 544 produced[1][2]
Assembly	Cricklewood, London
Designer	Walter Owen Bentley
Body and chassis
Class	Luxury car
Body style	as arranged with coachbuilder by customer[3]
Layout	FR layout
Powertrain
Engine	6.5 L I6
Dimensions
Wheelbase	132 in (3,353 mm)[4][5] 138 in (3,505 mm)[6] 140.5 in (3,569 mm)[5] 144 in (3,658 mm) 145.5 in (3,696 mm) 150 in (3,810 mm)[4] 151.5 in (3,848 mm) 152.5 in (3,874 mm)[4][5]
Chronology
Successor	Bentley 8 Litre

The regular Bentley 6½ Litre and the high-performance Bentley Speed Six were sports and luxury cars based on Bentley rolling chassis^[3] in production from 1926 to 1930. The Speed Six, introduced in 1928, would become the most successful racing Bentley. Two Bentley Speed Sixes became known as the Blue Train Bentleys after their owner Woolf Barnato's involvement in the Blue Train Races of 1930.

Background

By 1924, Bentley decided to build a larger chassis than the 3 Litre, with a smoother, more powerful engine. The new chassis would be more suitable for the large, heavy bodies that many of his customers were then putting on his sports car chassis, and the resulting car would be more refined and better suited for comfortable general motoring.^[1][7][8]

Prototype race

Bentley built a development mule with a 4¼ L straight-six engine^[7][8] derived from the 3 Litre's four cylinder engine.^[9] To disguise the car's origin, it had a large, wedge-shaped radiator^[8][9][10] and was registered as a "Sun".^[8][9] The car had a large Weymann-type^[9] tourer body built by Freestone and Webb.^[7]

W. O. Bentley combined one of his road tests of the Sun with a trip to see the 1924 French Grand Prix in Lyon.^[7] On his return trip to the ferry at Dieppe, W. O. encountered another disguised car at a three-way junction. W. O. and the Rolls-Royce test driver recognized each other and began racing each other along the routes nationale.^[7][9] This street race continued until the Rolls-Royce driver's hat blew off and he had to stop to retrieve it.^[8][9] The Sun's tyres were heavily worn when W.O. got to the ferry at Dieppe.^[8]

6½ Litre

1927 Bentley 6½ Litre
with H. J. Mulliner & Co. limousine body

rear view

Realizing from the impromptu race that the Sun had no performance advantage over Rolls-Royce's latest development,^[7] W. O. increased the bore of his six-cylinder engine from 80 millimetres (3.1 in) to 100 millimetres (3.9 in).^[8][9] With a 140 mm (5.5 in) stroke, the engine had a displacement of 6.6 L (6,597 cc (402.6 cu in))^[1][9][11] Like the four-cylinder engine, Bentley's straight-6 included overhead camshaft, 4 valves per cylinder,^[9] and a single-piece engine block and cylinder head cast in iron, which eliminated the need for a head gasket.^[12] In base form, with a single Smiths 5-jet carburettor,^[1] twin ignition magnetos,^[1][8][9] and a compression ratio of 4.4:1, the Bentley 6½ Litre delivered 147 horsepower (110 kW) at 3500 revolutions per minute.^[8][11]

Although based on the 3 Litre's engine, the 6½ engine incorporated many improvements. The 3 Litre's cone-type clutch^[13] was replaced by a dry-plate design^[5] that incorporated a clutch brake for fast gear changes, and the car had power-assisted^[1] four-wheel brakes with finned drums. The front brakes had 4 leading shoes per drum. By operating a patented compensating device, the driver could adjust all four brakes to correct for wear while the car was moving, which was particularly advantageous during races.

A large variety of wheelbases were produced for such a low-production car, ranging from 132 to 152.5 in (3,353 to 3,874 mm). The most popular wheelbase was 150 inches.^[4]

Speed Six

Old Number One, winner of the 24 Hours of Le Mans in 1929 and 1930

Speed Six tourer with original body by coachbuilder Hooper

The Bentley Speed Six was introduced in 1928^[5] as a more sporting version of the Bentley 6½ Litre.^[12] With a single-port block, two SU carburettors,^[5][8][11] a high-performance camshaft,^[14] and a compression ratio of 5.3:1, the Speed Six's engine produced 180 hp (130 kW) at 3500 rpm.^[5][11] The Speed Six was available to customers with wheelbases of 138 inches (3,505 mm),^[6] 140.5 inches (3,569 mm), and 152.5 inches (3,874 mm),^[5] with the 138 inch wheelbase being most popular.^[6]

The model was available as a road car for everyday use. Barnato 's personal Speed Sixes had bespoke bodywork by various coachbuilders, and the Criminal Investigation Department of the Western Australia Police operated two saloon-bodied examples as patrol cars.^[4]

In March 1930, Barnato raced against the Blue Train in a Speed Six with H. J. Mulliner saloon coachwork, reaching his club in London before the train was due in the station at Calais. It had generally been believed that the car in the race was a Gurney Nutting Sportsman Coupé, but the coupé had been delivered to Barnato in May 1930, more than a month after the race.^[15][16]

Factory racing cars

The racing version of the Speed Six had a wheelbase of 11 feet (132 in; 3,353 mm)^[5] and an engine with a compression ratio of 6.1:1 that produced 200 hp (150 kW) at 3500 rpm.^[17] Successful in racing, these cars won the 24 Hours of Le Mans in 1929 and 1930^[18][19] with Bentley Boys drivers "Tim" Birkin, Glen Kidston, and Woolf Barnato, the Chairman of Bentley Motors.^[19]

Production

• 6½ Litre: 362^[1]
• Speed Six: 182^[20]

Gallery

• 

  Woolf Barnato's Speed Six H. J. Mulliner saloon, in which he raced against the Blue Train

• 

  1930 Gurney Nutting Sportsman Coupé, often believed to be the car that raced the Blue Train despite being delivered to Barnato weeks after the race. Photo from 2009 Concours.

• 

  ...Another view

• 

  Bentley 6½ Litre Tourer

• 

  Bentley Speed Six drophead coupé

• 

  Bentley Speed Six prepared for racing

• 

  Bentley 6½-Litre Tourer

• 

  Bentley 6½-Litre Speed Six Tourer 1930

Notes

1. Brooks 2009, p. 27.
2. Johnson 2011, p. 9.
3. History By Chassis – List of all W. O. Bentleys with original chassis nos. 6 1/2 Litre (Page 1)
4. Brooks 2009, p. 28.
5. Robson 2001, p. 66
6. Brooks 2009, p. 31.
7. Feast 2004, p. 44
8. Johnson 2011, p. 8.
9. Posthumus 1977, p. 102.
10. Brooks 2009, p. 26.
11. Culshaw & Horribin 2013, p. 81.
12. Robson 2001, p. 68
13. Robson 2001, p. 60
14. Feast 2004, p. 46
15. "Special Edition: Bentley Arnage Blue Train", The Car Experience
16. Young 2010.
17. Johnson 2011, pp. 8-9.
18. Culshaw & Horrobin 2013, p. 82.
19. Feast 2004, p. 55
20. Brooks 2009, pp. 27-28.

References

Print

• Brooks, Philip C. (2009). Carpenter, Rhonda; Iwalani, Kahikina, eds. "The Mighty Sixes". The International Club for Rolls-Royce & Bentley Owners Desk Diary 2010 (Tampa, FL USA: Faircount): 26–35.
• Culshaw, David; Horrobin, Peter (2013) [1974]. "Bentley". The Complete Catalogue of British Cars 1895 - 1975 (e-book ed.). Poundbury, Dorchester, UK: Veloce Publishing. pp. 80–84. ISBN 978-1-845845-83-4.
• Feast, Richard (2004). The DNA of Bentley. St. Paul MN USA: MotorBooks International. ISBN 9780760319468. Retrieved 2013-12-24.
• Johnson, Harvey (Fall 2011). Verschoor, Ron, ed. "The Eight-Litre: Bentley's Last is Bentley's Best". The Classic Car (Beverley Hills, CA US: Classic Car Club of America) LIX (3): 3–11. ISSN 0009-8310.
• Posthumus, Cyril (1977) [1977]. The Story of Veteran & Vintage Cars. John Wood, illustrator. Feltham, Middlesex, UK: Hamlyn. p. 102. ISBN 0-600-39155-8.
• Robson, Graham (2001). The Illustrated Directory of Classic Cars. St. Paul, MN USA: MBI Publishing. pp. 66–69. ISBN 0-7603-1049-1. Retrieved 2013-12-27.

Online

• Young, Eoin (May 26, 2010). "Barnato, Bentley and the Blue Train Mystery – 190". New Zealand Classic Car Magazine (enthusiast's magazine). Retrieved December 31, 2013.
• "History By Chassis – List of all W. O. Bentleys with original chassis nos. 6 1/2 Litre (Page 1)". VintageBentleys.Org. Houston, TX USA: VintageBentleys.org. Archived from the original on 2009-04-13. Retrieved 2012-06-25.
• "Special Edition: Bentley Arnage Blue Train". The Car Experience. Barrie, ON Canada: Rayda Sinni. 2005. Archived from the original on 2011-07-16. Retrieved 2012-04-09.