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1931 Bentley 4.5 Litre

Walter Owen (W.O.) Bentley replaced the 3-Litre Bentley with the larger engined 4½ Litre in 1927. Production continued through 1931, and a total of 720 examples were built, including 55 (as few as 50) cars with a supercharged engine popularly known as the Blower Bentley.

1931 Bentley 4.5 Litre photo
Sports Tourer by Thrupp and Maberly
Along with the technically advanced prowess provided by W.O., the success of the early Bentley's was partly due to a group of passionate and extraordinarily wealthy young men, collectively known as the 'Bentley Boys', whose financial contributions sustained Bentley Motors and their accomplishments helped create the reputation on road and track. One of those individuals, Sir Henry Birkin, thought the powerful 4½-Litre model might benefit from a relatively new technique of supercharging. W.O. rejected the idea, but his company's chairman, Woolf Barnato, put the idea into production. These so-called 'Blower Bentley' received a specially shortened chassis to take advantage of the additional power. The supercharger was completely purpose-designed by Amherst-Villiers. Much of the funding for the project was supplied by Dorothy Paget, a wealthy sportswoman who had previously financed the Schneider Trophy-winning Supermarine seaplanes. The project was not without drama, as Bentley and Amherst-Villiers became involved in an argument over patent rights along with whose name it would wear.

Approximately 50 customer chassis were built, making the Blower something of a financial disaster, as the company had trouble selling that many. The first supercharged Bentley had been a 3-litre built during the close of 1926. The 4.5-liter Bentley produced 175 horsepower for the touring model and 240 horsepower in racing guise, which was more powerful than the Bentley 6½ Litre.

The Bentley's had found success at the 24 Hours of Le Mans endurance race. The inaugural race was held in May 1923 at the Circuit de la Sarthe. The 3 Litre Bentley won in 1924 and 1927. The Bentley 4½ Litre won in 1928, followed by a Speed Six winning in 1929 and 1930.

Motorsport Competition
Old Mother Gun
1927 Le Mans
The first team car fitted with the 4.5-liter engine was 'Old Mother Gun (chassis ST3001),' which was essentially a 3-liter team car fitted with a new cylinder block. Racing before official production began (Bentley introduced the 4.5 Litre in chassis form in October 1927 at the Olympia Motor Show), the larger and more powerful engine proved fast during the 1927 Le Mans race until the historic Maison Blanche crash that involved all three Bentleys and five other vehicles. Two of the Bentleys were forced to retire, with the third car continuing, although it was badly damaged. Drivers Dudley Benjafield and Sammy Davis managed to drive the 3 Litre Speed model to Bentley's second victory in the endurance classic with a definitive 20-lap margin. Bentley had won with a damaged car that required half an hour to repair in the pits.

1931 Bentley 4.5 Litre photo
Sports Tourer by Thrupp and Maberly
1928 Le Mans
Woolf Barnato and Bernard Rubin returned to Le Mans a year later with 'Old Mother Gun' and, after a race-long duel with the Stutz of Edouard Brisson and Robert Bloch, crossed the finish line in first place. The 4.5-Litre Bentley had won the race despite having a cracked subframe.

The 1924 Le Mans winner Frank Clement and the 1927 Le Mans winner Dudley Benjafield drove chassis number YW 2557 during the 1928 Le Mans race. It wore lightweight 'LeMans' coachwork by Vanden Plas with a body created from an ash frame with a fabric covering. At LeMans, it quickly recorded a new lap record of 72.7 mph. It was running in 4th place during the evening hours but a broken frame hampered its progress. It continued to limp along until a radiator hose broke a few laps later. Since racing regulations stated that water could only be replenished every twenty laps, YW 2557 was forced to retire on lap number 71.

1929
On May 10th and 11th of 1929, the 1927 Le Mans winner Sammy Davis shared driving duties with Gunter in the No. 6 4.5-liter Bentley (YW 2557). Clement and Cook drove another 4.5-liter Bentley (YV 7263), and Barnato and Benjafield drove a new Speed Six. The Speed Six was leading the race, averaging in excess of 92 mph, when it was forced to retire. The Bentley of Clement and Cook retired on the second day. The remaining Bentley (YW 2557) would battle with Alfa Romeo for first place, but when the checkered flag fell, the Bentley was in 2nd place.

1931 Bentley 4.5 Litre photo
Sports Tourer by Thrupp and Maberly
Old Mother Gun returned to Le Sarthe in 1929 and nearly repeated its victory, finishing in second place behind the newer and more powerful Bentley Speed Six Old Number One (6.5-liter engine). Five Bentleys had been entered in the race and only YV 7263 failed to finish. The roster included a singular Speed Six, Old Mother Gun, and the three other 4.5-liter team cars. At the close of the 24 hours, Bentley was in positions 1,2,3 and 4.

Additional accolades and victories achieved by the 4.5-Litre Bentley include a victory at the French Grand Prix and 500 miles of Brooklands in 1930.

The 1930 Bentley team had three Speed Sixes, which W.O. favored, while Birkin favored his personal project, the 'Blower' Bentley.

Mechanical Specification
The standard wheelbase used by the Bentley 4½ Litre measured 130 inches (3,300mm / 10 ft 10 in). Eight examples were built on the short wheelbase of 117.5 inches (2,980 mm). They had an overall length of 172.4 inches and a width of 68.5 inches. The lattice chassis was comprised of steel and reinforced with ties. The suspension was by semi-elliptic leaf springs and braking by 17-inch conventional drums that were finned for cooling and operated by rod.

1931 Bentley 4.5 Litre photo
Boattail by Gurney Nutting by Gurney Nutting
Chassis #: SM3916
Engine #: SM 3922
View info and history
Auction entries : 2
Engine
The engine displaced 4,398cc (268.4 cubic inches) and had a bore size of 3.9 inches (100 mm) and a stroke of 5.5 inches (140 mm). It had a cast iron block, dual ignition, Bosch magnetos, and a pair of SU carburetors. The crossflow, overhead camshaft actuated four valves per cylinder, rather than the traditional setup of two valves per cylinder used by many vehicles of the era. Bevel gears drove the camshaft on a vertical shaft at the front of the engine, similar to the design used on the preceeding 3 Litre engine. In the naturally aspirated configuration, the 268.4 cubic-inch engine produced 110 horsepower. Engines tuned for racing had around 130 horsepower. With the supercharger installed, output rose to 175 hp at 3,500 RPM for the touring model and 240 hp at 4,200 RPM in racing guise. The supercharged versions received a unique crankshaft, lubrication system, and pistons.

Blower Continuation Series
In 2019 and 2020, Bentley digitally re-created the Blower for a limited production 'continuation' series. They scanned all 630 components of the Blower and created 12 new models. The first example, dubbed the Blower Car Zero, was unveiled in December 2020. All twelve examples of the Blower Continuation Series were built in Crewe and faithfully followed the historical specifications and used the production processes of that era.


by Daniel Vaughan | Oct 2019

Related Reading : Bentley 4½ Litre History

The Bentley 4 12 liter came into existence to fill a void left by the 3-liter and the 6.5-liter variants. The 3-liter suffered from underperformance while the 6.5-liter was unsafe for the roads. The 6.5-liter was powerful, and with poor road-conditions often caused tires to fail quickly. The solution was the Bentley 4.5-liter a vehicle that had enough power to carry the vehicle down the road at....
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1931 Bentley 4.5 Litre Vehicle Profiles

1931 Bentley 4.5 Litre vehicle information
Tourer

Coachwork: Vanden Plas
1931 Bentley 4.5 Litre vehicle information
Four Seater Sports

Coachwork: Vanden Plas
Chassis #: MS3932
1931 Bentley 4.5 Litre vehicle information
Two-Seater Sports

Coachwork: Vanden Plas
Chassis #: MS3929
Engine #: MS3932
Gearbox #: 7241
1931 Bentley 4.5 Litre vehicle information
Sports Tourer

Coachwork: Thrupp and Maberly
Chassis #: MS 3928
Engine #: SM 3921
1931 Bentley 4.5 Litre vehicle information
Boattail by Gurney Nutting

Coachwork: Gurney Nutting
Chassis #: SM3916
Engine #: SM 3922
Build #: Supercharger No: 125
1931 Bentley 4.5 Litre vehicle information
Le Mans Boattail

Coachwork: Vanden Plas
Chassis #: MS 3944
Engine #: MS 3941
1931 Bentley 4.5 Litre vehicle information
Sports Tourer

Coachwork: Thrupp and Maberly
Chassis #: MR 3390
Engine #: MR 3393

Recent Vehicle Additions

Performance and Specification Comparison

4½ Litre

Specification Comparison by Year

Year
Production
Wheelbase
Engine
Prices
130.00 in.
4 cyl., 274.61 CID., 110.00hp
733
130.00 in.
4 cyl., 274.61 CID., 110.00hp
4 cyl., 274.61 CID., 182.00hp
130.00 in.
4 cyl., 274.61 CID., 110.00hp
117.50 in., 130.00 in.
4 cyl., 274.61 CID., 182.00hp

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