A Mark Wild and staff designed 1074 cc water-cooled four-cylinder engine with overhead valves announced August 1924[1] supplemented then replaced the Rover 8 air-cooled twin and the new vehicle was named 9/20[3] The new engine with its clutch and gearbox are mounted as a unit to the mainframe at four points.

[1] z Advertised by Rover as "The Nippy Nine" with emphasis on its water coolant circulated by pump, pressure lubricated engine, 3-speed gearbox and silent worm (rear) axle.

[5] The test car was the sports model with aluminium pistons, double valve springs, higher gear ratios and a lighter body.

The car was considered to run pleasantly and do around 60 mph in top gear.

The engine was thought to be unusually smooth for a two-bearing product even at high speed.