Bentley Demonstrator Blower
GH 6951 was one of just fifty road-going ‘Blower’ Bentleys built between 1929 and 1931 and was used as a demonstrator at the company’s offices in Cork Street. It was tested by The Autocar in September 1930, which ran with the subheading: ‘The Appeal of Immense Power, Linked with Great Docility’. With a Vanden Plas four-seater open tourer body the price of the Supercharged 4½ Litre was £1,720 in 1930.
The ’Blower’ Bentley
The 4½ Litre Supercharged ‘Blower’ Bentley divided opinion at Bentley. W.O. Bentley believed supercharging ‘perverted the engine’s design and corrupted its performance’, but Bentley Boy Sir Henry ‘Tim’ Birkin had been persuaded by independent engineer Amherst Villiers that supercharging offered the extra performance he demanded. He persuaded company Chairman Woolf Barnato to sanction the production of fifty supercharged Bentleys for sale to the public, to make his own team of four racing cars eligible for competition.
Engineering the Supercharger
Naturally aspirated, the Bentley 4½ Litre produced a relatively unstressed 100 bhp. With the supercharger, power leapt to 175 bhp in road-going form and 240 bhp in race tune. As a race engine the Blower was overstressed, but the road-going cars were reliable and tractable. The supercharger was crankshaft-driven and mounted in front of the radiator; other modifications included a heavier crankcase and cylinder block, stronger connecting rods, special pistons and gudgeon pins and revised engine mountings.
GH 6951
As a Bentley demonstrator, GH 6951 was tested by The Autocar in September 1930 and featured in the 1931 Gracie Fields film ‘Sally in our Alley’. Early in the car’s life the original engine was changed from MS 3921 to MS 3933 and the supercharger was also changed (from serial number 119 to 145). GH 6951 changed hands no fewer than four times between 1930 and 1939. Post–war, GH 6951 was bought in 1946 by E.J Griffiths, sold in 1947 to R.N. Dacre, again in 1950 to Bill Hardy and then in 1994 was acquired by the newspaper proprietor Eddie Shah. Since being acquired by Bentley Motors in 1997 it has taken part in numerous events and concours, including the Mille Miglia.
Specs & Details
| Date Produced | August 1930 |
| Chassis/engine no: | SM 3917 engine no. MS 3933 |
| Body | Vanden Plas open four-seater |
| Engine | 4-cylinders; 100 mm x 140 mm, 4398 cc. 4-valves, double springs; hollow overhead camshaft; cast-iron non-detachable cylinder head, cast iron cylinders; aluminium/Elektron crankcase, cam chest and sump. Amherst Villiers Mk IV roots-type supercharger |
| Power | 175 bhp (130 kW) @ 3,500 rpm |
| Transmission | Single dry plate clutch. D type gearbox |
| Chassis | 40-ton pressed steel frame, half elliptic leaf spring suspension; André friction dampers; Bentley-Perrot mechanical brakes, 15.75 in (40 cm) drums; worm and sector steering |
| Dimensions | Wheelbase 130 in (330.2 cm) |
| Performance | 97.8 mph. 0-60 mph 15 sec |
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