1931 Bentley 4½-liter ‘blower’ major service

The Bentley 4½-Litre Blower was born from Sir Henry "Tim" Birkin's conviction that supercharging, rather than increasing engine displacement, was the key to Bentley's success in international motorsport. W.O. Bentley opposed the idea, but Birkin received support from Dorothy Paget and commissioned Amherst Villiers to design a large Roots-type supercharger mounted in front of the crankshaft. To homologate the design for Le Mans, Bentley had to put fifty Blowers into production. These were completed between 1929 and 1931 and fitted with open tourer bodywork by Vanden Plas. In addition to these road-going versions, Birkin built five specially designed cars for the team in his Welwyn workshop, each with a stripped-down body, reinforced chassis components, and highly tuned engines. Four of the team cars competed in the 24 Hours of Le Mans in 1930 and 1931, where they were spectacularly fast but mechanically fragile. They often served as "pacers" to set the pace for the factory 6.5-liter Speed ​​Six. Although the Blowers never won a major endurance race, they became icons of British motorsport for their extraordinary speed and dramatic driving style. The production models, while less extreme than the team cars, offered remarkable performance for their time and quickly gained a reputation for their characteristic supercharger howl. Financial pressures and the stress of racing contributed to Bentley's bankruptcy in 1931, after which Rolls-Royce acquired the company and halted further development of the Blower. Despite their limited production run and inconsistent racing performance, the Blowers became some of the most celebrated Bentleys ever built, prized for their engineering prowess and unmistakable character. Their rarity, provenance, and connection to Birkin make both the production and Paget/Birkin team cars among the most sought-after pre-war British cars.

Technical specifications ('production blower')

Engine: Four cylinder engine OHC 4 valves per cylinder
cylinder capacity: 4398 cc
Induction: Amherst Villiers Mk IV Roots‑type supercharger mounted ahead of the crankshaft, dual S.U. carburettors feeding the supercharger
Petrol tank: 25 gallons (95 litres)
Ignition: Bosch or BTH dual coil/magneto with twin spark plugs per cylinder
Capacity: Approx. 175 bhp at 3,500 rpm (production Blower specification)
Top-speed: 110-115 mph (175-185 km/h) depending on gearing
Gearbox: Four-speed manual, non-synchromesh
Clutch: Single plate, manually operated
Brakes: Mechanical drum brakes on all four wheels, Bentley‑servo assisted
Suspension: Semi‑elliptic leaf springs with friction dampers at front and rear
Drive: Rear wheel drive
Wheels: Wire wheels with Rudge‑Whitworth centre‑lock hubs
Bodywork: Vanden Plas open tourer
Weight: Approximately 1700 kg.

Bentley history 1919 - 1931

The famous Bentley make, erected by Mr. W.O. Bentley, existed as a independent firm for only twelve years (1919-1931) before the proud firm was taken over by the Rolls Royce motor company. Those twelve exhilarating Bentley years were filled with racing successes and many important victories. The Bentley name as manufacturer of large, heavy, powerful and rugged sports cars has been imprinted in the human mind since the "roaring" 1920ies.

Bentley motorcars won the famous 24 hours of Le Mans race in the years 1924, 1927, 1928, 1929 and 1930. The years they did not win the long distance reliability race for production cars they finished second or third. Not only successes at Le Mans were counted but also victories in other long distance events like the Brooklands 500 mile race. The racing successes were mainly due to the rugged built of the cars and the meticulous preparation of the cars. In every race they learned and had the cars improved on small but important details (Head lamp covers, mesh gauze on the petrol tank, quick filler caps for engine oil and radiator, driver adjustable brakes.)

3-Litre

The Bentley 3 Litre was W.O. Bentley’s first design. The car was presented in 1919 but the first cars were sold in 1921. The four cylinder cars of rugged construction where in a class of their own for they combined the size and comfort of the big tourers and saloons with the road holding, and speed of the smaller sports- and racing cars. The Bentley was a true owner-driver car for the sporting motorist and connoisseur. The Bentley car could be had in three different types which were designated with three different radiator badges*. Red badge: short chassis speed model, Blue badge: the early short and then long chassis type for bespoke bodywork, Green badge: very rare and used for about eighteen 100 mph. These Green badge car won at Le Mans in 1924 and 1927 (Old Number Seven.) The 3-Litre was built from 1919 until 1929.

*The Bentley radiator and the logo were designed by the genius motoring artist Gordon Crosby. The logo is a ‘badge’ and not a ‘label’ as stated by AFC Hilstead in his book ‘Those Bentley Days’ (published 1953).

6.5 Litre and Speed Six

Then in 1926 the 6.5 Litre and the Speed Six were presented, these six cylinder models were in the eyes of W.O. Bentley the best cars the Bentley firm ever built. The bigger capacity was needed for many a customer had built a bespoke heavy saloon body on their chassis and thus eliminating the sporting element the chassis had to offer. The Speed Six brought Bentley the most racing successes and Le Mans victories. In the year 1929 the Speed Six came home first with Bentley 4.5 Litres second, third and fourth! In 1930 the same Bentley Speed Six 'Old Number one' came home a victor followed by another Speed six in second position!

4.5 Litre

Next came the upgraded four cylinder Bentley 4.5 Litre in the year 1927. The 4.5 Litre featured four valves per cylinder and two spark plugs per cylinder engine. Most of these cars were given open tourer and saloon bodywork and only nine short chassis were built.

4.5 Litre Supercharged (Blower)

The 4.5 Litre Blower was built in the ‘Barnato’ period. Financed by the Hon. Dorothy Paget Tim Birkin successfully experimented at Brooklands with his blower Bentley and even achieved the Brooklands lap record with his Blower Bentley. As Woolf Barnato was now in charge of the Bentley firm, and W.O. now only responsible for the development of the Bentley cars, Birkin convinced Barnato to enter a separate team of Blower Bentleys for the 1930 Le Mans race. This was against W.O. Bentley’s ideas for he was of the opinion that the supercharger would only add trouble to a perfectly good and reliable machine. The 1930 Le Mans race proved W.O. right as none of the blown cars finished and Barnato and Kidston won on a Speed Six model.
The supercharged 4.5 Litre engines were real "gas-guzzlers", the naturally aspirated 4.5 Litre engine used one litre of petrol every 5.6 kilometres, the supercharged engine used one litre for just 3.5 kilometres, a very large petrol tank was fitted additionally.
Another problem was that spark plugs in the supercharged engine wore out very quickly resulting in loss of power. Bentley engineer Nobby Clarke stated one day: "The blower eats spark plugs like a donkey eats hay". Only 55 Bentley 4.5 Litre ‘blower’ cars have been built by the firm of which 26 carried the Van den Plas open tourer bodywork.

8-litre

In 1931 the most impressive Bentley model ever saw the light of day; the 8-Litre. This car can be regarded as a real ‘super car’. Only 100 of these big cars have been built.

4- Litre

Also in 1931 a down scaled 8-Litre was introduced, the 4-Litre. The car was designed to sell more cars to improve the cumbersome financial situation at Bentley’s. The 1929 Wall Street crash affecting the firm immensely. The 4-Litre featured the chassis, transmission and brakes of the 8-litre. The newly constructed 120 bhp ‘Ricardo’ engine proved underpowered for the chassis and as a result the 4-litre never became the success Bentley hoped for. Only 50 chassis were built.

1931 Rolls Royce take over

In 1931 business prospects looked very black and the firm went into receivership. Napier & Son were negotiating with Bentley's receiver to take over the company. Then another interested party arrived at the scene named British Central Equitable Trust. They outbid Napiers in a sealed bid auction. The Trust later was found to be a front for Rolls-Royce Limited. Rolls Royce had cleverly defeated the threat of a firm that could become a very unwelcome competitor.

From 1933 all Bentley cars were based upon their Rolls Royce counterparts and production was then moved from Cricklewood to Derby. Purists tend to name the Rolls Royce produced cars – Rolls Royce Bentley’s. Rolls Royce took good care of the Bentley ‘marque’. Many magnificent automobiles were built with a distinctively different character than the Rolls Royce models.

_{© Marc Vorgers}