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.