Brumm R99; 1928 Bentley 4.5 Litre; 1928 24h Le Mans 1st; Barnato & Rubin, RN4

Between 1927 and 1931 the Bentley 4½ Litre competed in several competitions, primarily the 24 Hours of Le Mans. The first was the Old Mother Gun at the 1927 24 Hours of Le Mans, driven as a prototype before production. Favoured to win, it instead crashed and did not finish. Its performance was sufficient for Bentley to decide to start production and deliver the first models the same year.

Far from being the most powerful in the competitions, the 4½ Litre of Woolf Barnato and Bernard Rubin, raced neck and neck against Charles Weymann's Stutz Blackhawk DV16, setting a new record average speed of 111.12 km/h (69 mph); Tim Birkin and Jean Chassagne finished fifth. The next year, three 4½ Litres finished second, third, and fourth behind another Bentley, the Speed Six, which possessed two more cylinders.

The naturally aspirated 4½ Litre was noted for its good reliability. The supercharged models were not; the two Blower models entered in the 1930 24 Hours of Le Mans by Dorothy Paget, one of which was co-driven by Tim Birkin, did not complete the race. In 1930, Birkin finished second in the French Grand Prix at the Circuit de Pau behind a Bugatti Type 35. Ettore Bugatti, annoyed by the performance of Bentley, called the 4½ Litre the "fastest lorry in the world." The Type 35 is much lighter and consumes much less petrol. Blower Bentleys consume 4 litres per minute at full speed.