 The core of Bill Lyons' success following WWII was the twin-cam straight six engine, conceived pre-war and realised while engineers at the Coventry plant were dividing their time between fire-watching and designing the new power plant.It had a hemispherical cross-flow cylinder head with valves inclined from the vertical; originally at 30 degrees (inlet) and 45 degrees (exhaust) and later standardised to 45 degrees for both inlet and exhaust.As fuel octane ratings were relatively low from 1948 onwards, three piston configuration were offered