The Bentley 4½ Litre was a British car based on a rolling chassis built by Bentley Motors. Walter Owen Bentley replaced the Bentley 3 Litre with a more powerful car by increasing its engine displacement to 4.4 L (270 cu in).
Bentley buyers used their cars for personal transport and arranged for their new chassis to be fitted with various body styles, mostly saloons or tourers. However, the publicity brought by their competition programme was invaluable for marketing Bentley's cars.
At the time, noted car manufacturers like Bugatti and Lorraine-Dietrich focused on designing cars to compete in the 24 Hours of Le Mans, a popular automotive endurance course established only a few years earlier. A victory in this competition quickly elevated any car maker's reputation.
A total of 720 4½ Litre cars were produced between 1927 and 1931, including 55 cars with a supercharged engine popularly known as the Blower Bentley. A 4½ Litre Bentley won the 24 Hours of Le Mans in 1928. Though the supercharged 4½ Litre Bentley's competitive performance was not outstanding, it set several speed records, most famously in 1932 at Brooklands with a recorded speed of 222.03 km/h (138 mph).
The essential difference between the Bentley 4½ Litre and the Blower was the addition of a Roots-type supercharger to the Blower engine by engineer Amherst Villiers, who had also produced the supercharger. W. O. Bentley, as chief engineer of the company he had founded, refused to allow the engine to be modified to incorporate the supercharger. As a result, the supercharger was placed at the end of the crankshaft, in front of the radiator. This gave the Blower Bentley an easily recognisable appearance and also increased the car's understeer due to the additional weight at the front. A guard protected the two carburetters located at the compressor intake. Similar protection was used, both in the 4½ Litre and the Blower, for the fuel tank at the rear, because a flying stone punctured the 3 Litre of Frank Clement and John Duff during the first 24 Hours of Le Mans, which contributed to their defeat.
The crankshaft, pistons and lubrication system were special to the Blower engine. It produced 175 hp (130 kW) at 3,500 rpm for the touring model and 240 hp (180 kW) at 4,200 rpm for the racing version, which was more power than the Bentley 6½ Litre developed.