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1929-1931 Bentley 4½ Litre Birkin "Blower"


W.O. Bentley was not a fan of the idea of supercharging. When the notion was first suggested to him, he said: "It would pervert the design and corrupt its (the 4½ Litre's) performance." He was worried about reliability since supercharging or 'blowing' the engine doubled the car's power.


Supercharger engineer, Amherst Villiers, had been associated with Raymond Mays' Vauxhall Villiers Supercharge – a sprint car based on the 1922 TT Vauxhall. The Bentley directors had previously commissioned him to design a Bentley (of which W.O. disapproved).


Bentley Boy Sir Henry 'Tim' Birkin persuaded Bentley's Chairman, Captain Woolf Barnato, to enter a team at Le Mans in 1930, obliging the company to make 50 for sale. Work was done at Birkin's workshops at Welwyn Garden City, belonging to racehorse owner Dorothy Paget. By 1929 sales of the regular 4½ Litre were declining, so there was some logic in extending the life of the 4-cylinder by adding a Roots-type supercharger driven off the crankshaft between the front dumb-irons.


It meant significant engine modifications, including a heavier crankcase and cylinder block, stronger connecting rods, special pistons, and in the racing versions, a counterbalanced crankshaft. But as WO said ruefully, "… the supercharged 4½ never won a race, suffered a never-ending series of mechanical failures and brought the marque, Bentley, into disrepute".


While the supercharged Blower didn't ever win at Le Mans, with Tim Birkin at the wheel, its heroic performance embodies the true spirit of the vintage racing era. In the 1930 race, Birkin and his Blower diced for the lead with Mercedes ace, Rudi Caracciola, passing him flat out down the Hunaudières straight with his nearside wheels on the grass. But neither Birkin's Blower nor the Mercedes could maintain the pace, and Barnato and Kidston won the race in their Bentley Speed Six.