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Lot 691: 1930 Bentley 4½-Litre Supercharged Tourer

Collectors' Motor Cars and Motorcycles, Bonhams (3 December 2007)

The car offered here is a wonderful example of that most sought after of all W O Bentley models: the legendary 4½-Litre Supercharged, or ‘Blower’. First shown at the 1929 London Motor Show, the ‘Blower Bentley’ was developed as a private venture by ‘Bentley Boy’ Sir Henry Birkin in order to extract more performance from the proven 4½-Litre model, which was becoming outclassed by its rivals on the racetracks of Europe. His aim was to produce a British car that would enable British drivers to continue to win races as spectacularly as the 4½-Litre that had won the 1928 Le Mans 24-Hour race.
The supercharger installation was engineered by the brilliant Amherst Villiers, who modestly claimed that it was ‘recognised in engineering circles as a definite landmark in automobile construction.’ Unimpressed, W O Bentley never supported the development of the supercharged car and is quoted as saying how much he ‘disliked the easy short cut provided by the supercharger,’ preferring to increase engine capacity, as evidenced by the 6½-Litre and 8-Litre cars, while reducing front-end weight by using Elektron castings. However, ‘W O’ did not control the purse strings at Bentley Motors, and the influence of Birkin, backed by the fabulously wealthy Woolf Barnato, saw the supercharged 4½-Litre Bentley come to fruition. Its potential was emphatically demonstrated when Tim Birkin took 2nd place in the French Grand Prix at Pau with his supercharged 4½-Litre tourer amid a field of monoposto GP racers.
The production cars were fitted with an Amherst Villiers Supercharger Mark IV, of Roots type with twin paddle rotors, which drew mixture from twin SU carburettors and was driven off the front of the crankshaft, the latter having been substantially strengthened to accommodate the increased power. With 9½lbs boost at 3,500rpm, the blown Bentley developed 175bhp, a healthy increase over the production 4½-Litre’s 110 horsepower, while with 10lbs boost at 3,900rpm, 182bhp was produced. The first production model, chassis number ‘SM 3903’, a sporting four-seater bodied by Vanden Plas, was exhibited on Stand 130 at The Motor Exhibition at Olympia in October 1929 and would be retained as the Company demonstrator. Although similar in many respects to the standard 4½-Litre car, the new model was immediately distinguishable by the massive supercharger protruding at the base of the radiator.
Just 50 production supercharged 4½-Litre Bentleys were built to support the homologation of five Birkin team cars: among the few cars of their day capable of 100mph on the open road, they have always been regarded as the supercars of their era. Motor Sport spoke of the Blower’s ‘remarkable acceleration’ and ‘ancestry of well-tried racers’ and called it ‘a car for the connoisseur of sporting cars...’
Chassis number ‘SM3914’ is the 14th of the 50 production supercharged 4½-Litre cars manufactured by Bentley Motors in 1930/31. The accompanying report on ‘SM3914’, prepared by recognised marque authority, Michael Hay and dated 1st December 2002, from which we draw extensively below, states that the first 25 chassis, including ‘SM3914’, were fitted with a plain supercharger centre casing, which was changed to a ribbed pattern for the second batch of 25 chassis (‘MS3926-3950’). Most of the earlier cars were converted and ‘SM3914’ is one of the few still fitted with a plain-case supercharger. The engine originally fitted to chassis ‘SM3914’ was ‘SM3917’, this sort of variation between engine and chassis numbers being typical of Bentley Motors’ production practice.

According to Bentley Service Record notes, ‘SM3914’ was finished on 19th June 1930 and sent to Vanden Plas to be bodied. The Vanden Plas body (number ‘1614’) was a special panelled Weymann sports coupé, built for exhibition on the coachbuilder’s stand at the 1930 Olympia Motor Show. After the Show, ‘M3914’ was registered ‘GK 3840’ and sold by Rootes to Mr Jack Howarth of Cheshire; the Service Record dates the guarantee from 8th October 1930. The Service Record lists the car on delivery as a 1931 Model, though it is not known what work, if any, was done to bring it up to 1931 specification. Howarth kept the car until 23rd February 1934, when he sold it to Jack Barclay Ltd. By this time the colour scheme had been changed to green over black. Barclay’s sold ‘SM3914’ to another dealer, William Arnold Ltd, on 1st September 1934 and Arnold’s sold the Bentley on to one A L Dyer later that year. During Dyer’s ownership the Service Record notes some work after an accident in December 1934, requiring a reconditioned petrol tank and back axle banjo. The Service Record is continuous through to 1939, the last entry noting a change of ownership to an O F Ellison, of Derby. The Service Record notes changes in the registration number to ‘SG 1’ (date not known) and then to ‘DS 2123’ (a 1937 Peebles number).
As usual, there is then a gap in the records until ‘SM3914’ reappears after the war. The first entry in Bentley Drivers Club records is for January 1950, when ‘SM3914’ was owned jointly by Capt M L and Lt Cdr C P Morgan-Giles. Offered for sale by well-known dealer Cecil Bendall in 1951, the next recorded owner is M R Grist in June 1952 followed by D G McClure in July 1953. When bought by Mr McClure ‘SM3914’ was still in very original order, but its new owner wanted a sporting car, so he almost immediately removed and scrapped the body, fitting an open four-seater one in its place. McClure raced the car extensively, and during his ownership the original blower-pattern 10’ 10”-wheelbase chassis frame was removed and scrapped, replaced by a 9’ 9½” chassis frame taken from another 4½-Litre car. This chassis was fitted with the ‘blower’ front cross-member and tie bar from the original chassis frame ‘SM3914’, thus erasing the identity of the replacement 4½-Litre frame fitted, although it is believed to be ‘FT3214’. At some point McClure also removed the supercharger unit, and for some reason the supercharger drive spigot on the front of the crankshaft was cut off. ‘SM3914’ was also converted to hydraulic brakes.
In July 1967 McClure sold ‘SM3914’, which over the next quarter-century passed through a number of hands before being purchased by the current owner in 2001. By this time it had been rebuilt more than once and came with supercharger refitted, Birkin replica body (made by Townshend), 50-gallon Birkin-style petrol tank and back to mechanical brakes.
In its current form, ‘SM3914’ has the standard 4½-Litre chassis frame fitted with bolted strut-gear, original front cross-member (numbered ‘SM3914’) and tie-bar, original ‘Blower’-pattern radiator and original front axle beam numbered ‘SM3914’. The original having been extensively damaged, the engine has been rebuilt using various new parts including the crankcase, sump and heavy pattern ‘Blower’ cylinder block. The magneto turret (numbered ‘SM3917’) is original, and the un-ribbed supercharger unit - numbered ‘114’ in small numerals on the front of the casing, as per Bentley Motors practice - is of the correct type. Although stamped ‘SM3914’, the steering column is from another Bentley (the original steering column numbered ‘SM3914’ is in a 3-Litre, chassis ‘479’). The D type gearbox (number ‘7220’) is the car’s original, while the rest of the transmission comprises a plate clutch with appropriate pedals; heavy pattern Spicer shaft; correct-type 6½-Litre pattern differential (number ‘BX2417’) and 4½-Litre banjo (number ‘KM3082’). The new Le Mans replica body is the work of H & H Coachbuilders while the fittings, bonnet, wings, stays, instruments (except original switch plate), shock absorbers and the Birkin-style petrol tank likewise are new. Sensible upgrades commissioned by the current owner include overdrive transmission, alternator electrics and sealed-beam headlight units.
Considerable mechanical refurbishment (invoices available) was undertaken by the immediately preceding owner, and the vendor has continued this process, bringing ‘SM3914’ to the peak of perfection over the course of the past few years. Much of this recent renovation has been entrusted to specialist vintage car restorer, W J Huckle, of Sleaford, Lincolnshire (in excess of £40,000), with further work by R Harcourt-Smithof Headley, Berkshire (in excess of £10,000), and with G J Peters restorations of the Netherlands (in excess of £20,000). So, recent invoices totalling well over £70,000 are on file, which highlights that every aspect of this car has been overhauled to the highest of standards.
‘Blower’ Bentleys rarely come on the market and thus ‘SM3914’ represents a possibly once-in-a-lifetime opportunity to acquire one of these charismatic cars, presented in perfect condition throughout, ‘on the button’ and ready to drive away.

Lot Details
Auction Collectors' Motor Cars and Motorcycles
Bonhams, Olympia, London,
Lot Number691
Outcome NOT SOLD
Hammer Price-
Hammer Price (inc premium)-
Condition rating
Registration number
Chassis numberSM3914
Engine numberSM3917
Engine capacity (cc)
Engine - cylinders
Number of doors