1931 Bentley 4 1/2 Litre


  • Year of manufacture 
  • Chassis number 
    SM 3925 (see text)
  • Engine number 
    SM 3928
  • Lot number 
  • Drive 
  • Condition 
  • Number of seats 
  • Location
  • Exterior colour 
  • Drivetrain 
  • Fuel type 


1 of the 50 originally built
1931 Bentley 4½-Litre Supercharged Tourer
Registration no. GW 2222
Chassis no. SM 3925 (see text)
Engine no. SM 3928

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'. 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.

Only 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...'

Retaining its original registration, GW 2222, chassis number 'SM 3925' was the last of the first batch of 25 production supercharged 4½-Litre cars manufactured by Bentley Motors in 1930/1931. Completed in June '31, it is one of only five 'Blowers' originally delivered with saloon coachwork: three (including 'SM 3925') being bodied by Freestone & Webb and one each by Maythorn and Gurney Nutting. The first 25 chassis, 'SM 3925' included, 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 but 'SM 3925' is one of the few still fitted with a plain-case supercharger, albeit not its original unit; the supercharger fitted (number '121') is from the 1930 Olympia Show car, 'SM 3920'. The engine originally fitted to chassis 'SM 3925' was 'SM 3928', this sort of variation between engine and chassis numbers being typical of Bentley Motors' production practice.

This particular 'Blower' was ordered from Jack Barclay's London showroom by one Terence Byron of Whaley Bridge, Cheshire, as evidenced by a copy of the original order document on file. Chassis records (copies available) list the next owner as one L K Cornish of London N9 followed by G J Dawson of Lambeth, Southwest London.
In 1935, apparently still owned by Dawson, the Bentley was returned to the works for repair following an accident. As was Bentley Motors' practice, many of the parts used in the rebuild had been taken from other cars and reconditioned before being put back into service.

The factory record states 'chassis frame reconditioned', which usually indicates the fitment of a previously used replacement chassis frame from Bentley Service Department stock. Further parts also fitted at this time included a new front axle bed, new dumb irons, new top steering arm and front anchor plate, new offside stub axle, new steering wheel and worm wheel shaft. Two new Lucas headlights and a pair of new front road springs were also fitted and the radiator reconditioned. Later, in November 1938, the factory supplied a replacement D-Type gearbox: D-7015 for the car.

Component swaps are by no means uncommon among Cricklewood-era Bentleys, and this car's original engine later found its way into 3-Litre chassis number 'HT1633', while the reconditioned front axle and steering box taken from 'SM 3925' were fitted to 4½-Litre chassis 'HF 3196'. Fitted with a two-seater body and owned by Kemp Place, 'HF 3196' was raced by him throughout the late 1940s/1950s.

In 1984, the ambitious project to return 'SM 3925' to it's former glory commenced, sourcing and ultimately utilising as many of the original components as possible, a Herculean task that would take many years to complete. During this period of ownership a genuine and original period heavy gauge chassis frame was fitted with engine 'SM 3928', sourced in 1989 and then a few years later, the sale of the ex Place racer, known as 'Black Bitch', brought with it the opportunity to acquire the original front axle and steering box. A suitable D-type gearbox was found - 'D-7026 - amazingly only 11 numbers away from the 1938 replacement.

The rear axle was sourced using the common practice of using an original and genuine Bentley 6½-litre unit - the differential unit was originally fitted to Speed Six chassis number 'NH 2728' - and the rear axle banjo is from a 6½-litre saloon - chassis number 'FW 2602' - which had been subject to a rear axle change at the factory in November 1934, suggesting this axle had been already been recycled, reprocessed and subsequently used in another car in the interim time.

Of all the components that make up a 'Blower' Bentley it is the supercharger, that presents the greatest difficulty for restorers; fortunately, the Olympia Show car's unit was located in the USA and purchased. It was decided to rebuild the car with the enduringly popular Vanden Plas Team Car-style tourer coachwork.
Since the rebuild's completion in 1993, 'SM 3925' has been enthusiastically enjoyed by only two owners, and in 2010 joined 17 other 'Blowers' in Switzerland to celebrate the 80th anniversary of the model's debut at Le Mans. 'SM 3925' performed faultlessly on this fabulous Alpine tour, of course driving down from England and taking the long way home to include a visit to the LM Classic, where it was immediately waved straight through and directed in to the paddock with the competing Vintage Bentleys that year. Accompanying documentation includes the 1990 FIVA card, 1994 FIA papers, 2012 FIVA Identity Card, and the aforementioned copy factory records, etc.

'Blower' Bentleys rarely come on the market and thus 'SM 3925' represents a possibly once-in-a-lifetime opportunity to acquire one of these charismatic cars, presented in excellent condition throughout, 'on the button', and ready to drive away. A welcome invitee to the world's most prestigious and exclusive historic motoring events, there can be no better way to enjoy the many celebrations planned for Bentley's 100th anniversary in 2019.