Often confused with the Speed 6, the 6½ Litre was Bentley’s first large-displacement, six-cylinder car. The new engine was necessary to bolster the image of Bentley beyond rivals of Rolls-Royce and Mercedes-Benz. Furthermore, the six-cylinder unit ran much smoother than the 6½. The new engine was very advanced, using aluminum pistons and a unique valvetrain that employed the use of three crankshafts.
Although intended for luxury, the advanced engine was raced with great success in the Speed 6.To keep pace with the larger engine, the chassis was upgraded. Larger disc brakes were fitted with finned aluminum drums. The first 6½ appeared as a bare chassis at the 1925 Olympia Motor Show, but it would take over a year to launch the car. During this period the engine was thorougly tested and bored out to 6,597cc before market launch.