The Rolls-Royce 20/25 HP Sport Saloon by J. Mulliner & Co from 1934, 3680 cc, max. speed 120 km/h
The Rolls-Royce 20/25 was the second of Rolls-Royce Ltd’s pre-war entry level models. Built between 1929 and 1936, it was tremendously popular, becoming the most successful selling inter-war Rolls-Royce. Its success enabled Rolls-Royce to survive the economic difficulties of the Great Depression years and remain one of world’s great brands. A total of 3,827 20/25s were produced, of which over 70% are still on the road today.
The 20/25 was the successor of the highly successful 20 hp Rolls-Royce Twenty introduced in 1922. The target market for the 20/25 was the same as the Twenty – the luxury, owner driver market. The project to develop the next generation 20 hp was code named Goshawk. The goal for the new model was to increase power & performance.
This was achieved by increasing the bore size from 3 to 3.25 inches. The stroke was unchanged at 4.5 inches. This resulted in a 17% increase in capacity from 3128 to 3675cc – bring the RAC rating up to 25.4 hp.
Engine: In-line 6-cylinder, overhead pushrod operated valve engine with 3699cc capacity. Separate cast iron block and aluminum crankcase with detachable cast iron 6-plug head. It has an 82 mm bore with a 114 mm stroke. 7-bearing crankshaft with vibration damper. Pressure fed lubrication with relief valve feeding rocker shaft and timing gears.
Ignition System: Independent coil and standby magneto systems. 12V system 50 Amp/Hrs battery. Centrifugal advance with hand override. Distributor gap 0.017-0.021inches
Cooling System: The famous Rolls-Royce radiator with triangular top with vertical louvres, the angle of which can be adjusted to control engine cooling. To begin with, the radiator shutters were operated manually via a lever on the dash; after 1931 cars were fitted with automatic control via a thermostat. Engine driven centrifugal pump and belt-driven fan.
Carburation: A single Rolls-Royce 2-jet type with starting carburetor, automatic air valve and steering column control.
Fuel: 14 gallon rear tank increased to 18 gallon tank starting in 1932. Autovac (vacuum fed) fuel pump and an electric fuel gauge (starting in 1933).
Transmission: 4-speed gearbox, synchromesh in 3rd and top from 1932. Right hand gearchange. Single dry plate clutch. Open drive propeller shaft.
Suspension: Semi-elliptic leaf springs front and rear. Hydraulic dampers.
Brakes: Internal expanding 4 wheel operation with independent handbrake on the rear wheels. Mechanical servo motor driven from the gearbox.
Chassis lubrication: “One-Shot” Bijur centralized chassis lubrication system.
Steering: Worm and nut. (1936, Marles cam and roller – GTK 42).
H. J. Mulliner & Co. was a well-known British coachbuilder operating from Bedford Park, Chiswick, West London. The company which owned it was formed by H J Mulliner in 1897 but the business was a continuing branch of a family business founded in Northampton in the 1760s to hire out carriages. In December 1909 the controlling interest in this company passed to John Croall & Sons of Edinburgh. Croall sold that interest to Rolls-Royce in 1959.
“Mulliner” is now the personal commissioning department for Bentley.