The regular Bentley 6½ Litre and the high-performance Bentley Speed Six were Bentley automobiles in production from 1926 to 1930. They were created out of the desire for more engine power by Walter Owen Bentley by adding two cylinders to the straight-4 engine used in his Bentley 4½ Litre car. The Speed Six, introduced in 1928, would become the most-successful racing Bentley. Two Bentley Speed Six became known as the Blue Train Bentleys for their owner Woolf Barnato’s involvement in the Blue Train Races of 1930.

The Bentley 4½ Litre is a British sports car built by Bentley Motors. Its supercharged variant is also known as the Blower Bentley. Famous for his statement “there’s no replacement for displacement”, Walter Owen Bentley upped the displacement of the Bentley 3 Litre in 1926 to produce the 4½ Litre. Upon taking control of the company, the “Bentley Boys” went in search of even more power and developed the supercharged model in 1929 at Henry Birkin’s racing workshops in Welwyn Garden City.