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1929→1931 Bentley 4½ Litre Blower

1929→1931 Bentley 4½ Litre Blower

With it’s front mounted supercharger, the 4½ became one of Walter Owen Bentley’s quintessential British sportscars. It was the vision and product of Sir Henry Ralph Stanley ‘Tim’ Birkin who persuaded Bentley to produce 50 examples of the model.

The company Birkin & Couper Ltd. was established to specifically supercharge Bentley’s four-cylinder cars despite W.O. Bentley’s apprehension. W.O. Bentley said “They would lack in their preparation all the experience we had built up in (our own) racing department over 10 years. I feared the worst and looked forward to their first appearance with anxiety.”

Unblown, the standard 4.5 liter engine put out 110HP. The use of a Roots supercharger offered an increase in power to 240 bhp. The power was necessary due to the massive size and weight of the car.

The overall design of the car was heavy and large. The tall engine forced the driver to sit with his head 63 inches above ground. To help compensate for a high center of gravity & weight Bentley employed the use of stiff and heavily damped springs. Excessive weight of the car due to huge brakes, large chassis & a bulky rear axle put the car in a class of its own. The Blower is one of the heaviest cars to compete in racing.

The first single seat prototype was initially built in 1929 with racer Mike Couper. The finished product was a 1½-seat Bentley with a massive 10 feet 10 inch wheelbase. It had a fabric skin stretched over steel structure that barely covered the components. It became the fastest racecar in Britain by holding the Brooklands Outer Circuit Lap Record in 1930.

Birkin established Birkin & Couper Ltd. where the first Blowers were made. W.O. Bentley said “They would lack in their preparation all the experience we had built up in (our own) racing department over 10 years. I feared the worst and looked forward to their first appearance with anxiety…”

The first appearance of the car was the Brooklands 6-Hour race on June 29,1929. Later in the year more 4½ Litre Bentleys were fitted with Birkin’s blower system and one placed second in the RAC Tourist Trophy, but they never won a race.

Bentley described the model at the end of the season “The supercharged 4½ never won a race, suffered a never-ending series of mechanical failures, brought the marque Bentley disrepute and incidentally cost Dorothy Paget a large sum before she decided to withdraw her support in October 1930…”

Despite the lack of results, Wolf Barnato allowed Birkin to try the cars again at Le Mans but none of them endured to finish. This meant Bentley was obliged to produce 50 road going examples of the model which they did.

The number 9 car featured above, UU5872, is an original Birkin car known as ‘Birkin Blower No.2’. This car made an appearance at the 1930 Lemans. The first car featured above is an unrestored 1928 works blower.

In Detail

tags 4.5
submitted by Richard Owen
type Series Production Car
production years 1929 – 1931
engineers Walter Owen Bentley
production 55
engine Inline-4
aspiration Amhurst Villiers Roots-Type Supercharger
block material Cast Iron
valvetrain SOHC 4 Valves / Cyl
fuel feed 2 SU HVG5 Carburettors
displacement 4398 cc / 268.38 in³
bore 100 mm / 3.94 in
stroke 140 mm / 5.51 in
power 130.5 kw / 175 bhp @ 3500 rpm
specific output 39.79 bhp per litre
bhp/weight 90.67 bhp per tonne
body / frame Fabric Body over Steel Ladder-Type Chassis
driven wheels RWD
front tires Dunlop 6×21
rear tires Dunlop 6×21
front brakes Mechnical Drums
rear brakes Mechnical Drums
front wheels F 53.3 x 15.2 cm / 21.0 x 6.0 in
rear wheels R 53.3 x 15.2 cm / 21.0 x 6.0 in
steering Worm & Wheel
f suspension Solid Axle w/Semi-Elliptic Leaf Springs, Friction Dampers
r suspension Live Axle w/Semi-Elliptic Leaf Springs, Friction Dampers
curb weight 1930 kg / 4250 lbs
wheelbase 3302 mm / 130.0 in
front track 1384 mm / 54.5 in
rear track 1384 mm / 54.5 in
length 4369 mm / 172.0 in
width 1740 mm / 68.5 in
height 1600 mm / 63.0 in
transmission 4-Speed Manual
top speed ~209.2 kph / 130.0 mph

Auction Sales History


1931 Bentley 4½-Litre Supercharged Two-Seater Sports MS3929

One of the 50 original supercharged “Blower” Bentleys. Original chassis, engine, D-type gearbox, and supercharger. The last “W.O.” Bentley bodied in period by Vanden Plas; offered with its original coachwork. Available after nearly 30 years of continuous family ownership. Documented and authenticated by Bentley historian Dr. Clare Hay. A veteran of the Mille Miglia Storica; complete with FIA paperwork. Exceptional purity; one of the finest ever offered.

Auction Source: RM Sotheby’s Monterey 2015

1931 Bentley 4½ Liter Supercharged Le Mans MS 3944

One of three Original Le Mans Specification production Supercharged cars built. Owned by the Noble family for more than 55 years. Original components and numbers as delivered new from Bentley. Documented by Bentley Expert Dr. Clare Hay. Eligible for Mille Miglia and more.

Auction Source: 2013 Quail Lodge Auction by Bonhams

1931 Bentley 4½ Litre ‘Blower’ Sports 2/3 Seater Boattail SM3916 – did not sell for $7,100,000 Among the Finest of the 50 Factory Blowers. Exceedingly Rare, Matching-Numbers, Original-Bodied Example. Exceptional Provenance Including a 54-Year Stewardship. One of Very Few Vintage Bentleys with Original Fabric Covering. Ideal International Driving and Concours Event Entrant. One of the Most Significant Bentleys in Existence
Auction Source: 2012 Pebble Beach Auctions by Gooding & Company

1929 Bentley 4½ Litre ‘Blower’ Single-Seater

It is now offered here as an exceedingly potent reminder of a magisterial period of British racing history, a machine with a unique place in racing history, and the exception to the W.O. Bentley ‘rule’ that “…the supercharged 4½ never won a race”.

Auction Source: 2012 Goodwood Festival of Speed


1929 Bentley 4½-Liter Supercharged DS3569

The immediately preceding owner bought ‘DS 3569’ in the late 1980’s, the car having been in the previous ownership for some 24-or-so years. At that stage it was in driveable but weary condition, and a decision was taken to carry out a complete restoration, transforming the car as closely as possible to the specification of Birkin’s supercharged 4½-Liter Team Cars. This was to be a meticulously researched and expertly executed task taking some ten years to complete, the car’s fastidious owner overseeing every aspect and drawing expertise from only the most experienced ‘W O’ Bentley specialists.

Auction Source: 2009 Bonhams Exceptional Motorcars at Quail Lodge Resort