Following the 6½ Litre released in 1926, Bentley thoroughly updated the design with a more powerful engine. This flagship model was bodied by the best British coachbuilders and also raced with great success alongside the 4½ Litre. It was Walter Owen Bentley’s favorite model and became the firms most successful car on the track.
Bentley gained much respect after proving their endurance at the 24 Hours of Le Mans and winning many English races including the Tourist Trophy and Brooklands Double 12. In fact, Bentley was at the very first 24 Hours held in 1923, and won the event in 1924, 27, 28, 29 and 30. These later victories were achieved with specially fitted Speed Sixes which was one of Walter Owen Bentley’s favorite cars.
The basis for all of Bentley’s cars was an engine which in many respects was ahead of its time. Drawing upon experience gained from working at the Great Northern Railway and designing airplane engines, Walter Owen Bentley included such characteristics as aluminum pistons, dry-sump lubrication, twin spark ignition and an advanced valve train in his engines. Early models featured four cylinders and after 1925, Bentley released a straight six which would become his highlight work, and provide necessary power for heavy coachwork and grand touring. Exapnding on the ½ Litre, the main upgrade for a Speed 6 was a square-section intake manifold that increased power from 147 to 160 bhp and later 180 bhp with a slight redesign using a single port.
All Speed Sixes are identified by their parallel-sided radiator and green enamelled badges unlike the standard blue label for the 6½ Litre.
| type | Series Production Car |
| production years | 1929 – 1930 |
| released at | 1928 Olympia Show |
| built at | England |
| engineers | Walter Owen Bentley |
| engine | Inline-6 w/Twin Spark Ignition |
| position | Front Longitudinal |
| aspiration | Natural |
| block material | Cast Iron |
| valvetrain | SOHC, 4 Valves per Cyl |
| fuel feed | Carburetors |
| displacement | 6597 cc / 402.57 in³ |
| bore | 100 mm / 3.9 in |
| stroke | 140 mm / 5.5 in |
| compression | 5.3:1 |
| power | 134.2 kw / 180 bhp |
| specific output | 27.29 bhp per litre |
| body / frame | Steel Chassis |
| driven wheels | RWD |
| front brakes | Drums |
| rear brakes | Drums |
| f suspension | Solid Axle w/Semi-Elliptic Leaf Springs, Friction Dampers |
| r suspension | Live Axle w/Semi-Elliptic Leaf Springs, Friction Dampers |
| transmission | 4-Speed Manual |
