Rolls-Royce 25/30
The Rolls-Royce 25/30 built between 1936 and 1938 is an updated version of the 20/25 with larger engine to provide more power, as over-large bodies had often been fitted to the earlier model leading to complaints about its performance.
Engineering
The in-line 6-cylinder, overhead-valve 25/30 hp engine is similar to that used in the 20/25 but increased in capacity to by increasing the bore from to, with the stroke remaining at. The compression ratio is 6:1. A single proprietary Stromberg downdraught carburettor replaced the Rolls-Royce one, and magneto ignition was no longer fitted, but a standby coil was provided. The four-speed gearbox is mounted in unit with the engine, and a traditional right-hand change used. Synchromesh is fitted to third and top gears.The riveted chassis has rigid front and rear axles suspended by half-elliptic springs with hydraulic dampers. Braking is on all four wheels assisted by a mechanical servo, famously under licence of Hispano-Suiza. Separate rear brakes are fitted for the handbrake. The traditional Rolls-Royce radiator with triangular top was used with vertical louvres, the opening angle of which is controlled thermostatically to control engine cooling.