The Rolls-Royce 25/30 built between 1936 and 1938 is an updated version of the 20/25 with a larger engine to provide more power, as over-large bodies had often been fitted to the earlier model leading to complaints about its performance.[2]
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 4257 cc by increasing the bore from 3.25 in to 3.5 in, with the stroke remaining at 4.5 in. 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.[1] 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.