ROVER 21hp Six

Although Autocar on 19 October 1923 reported on the presentation of the car on the occasion of the Olympic show, little is known about the 3½ litre limousine developed by Mark Wild. However, it was almost certainly Rovers' first attempt at a six-cylinder model. The engine was derived from the Clegg-designed 12 hp, which had the same 75 mm x 130 mm bore and stroke dimensions. The 3446 cc car would have received a RAC rating, returning Rover to the class it already had from 1908 with the 20 hp derivatives of the 16/20hp.

The car was also the first rover with four-wheel brake according to the Perrot system. It had a right-hand four-speed transmission and an oil-running double disc clutch, the engine had valves arranged side by side, a low-noise chain-driven camshaft and a removable cylinder head. The cooling water circulation with pump was thermostat-controlled, the pressure lubrication supplied all five crankshaft bearings as well as the connecting rod bearings. The underslung rear axle, which is driven by an open cardan shaft, is equipped with a worm drive, as is usual with rovers. The chassis has semi-elliptical springs and D.N. shock absorbers. With a wheelbase of 3480 mm and a track width of 1422 mm, the 3½-liter was by far the largest car Rover had ever built and, as the illustration also shows, was fitted with a spacious closed Weymann body and weighs only 1320 kg.

The sparse sources indicate that only three cars were built. But the real reason why the 21hp didn't go into production remains a mystery. One theory is that the public response to the 1923 Olympic Show was lukewarm; another is that when Peter Poppe joined Rover as chief engineer, he wanted to use his own design for the company's new big car, not another's. Either way, the 3½-liter design seems to have had some influence on the 14/45 hp models and the subsequent 16/50 hp.

"The Engineer" of 9 November 1923 reports about the ROVER 'Six':

Sources
	Report in The Engineer, dated 9 November 1923
	Image from an article in MotorSport, November 1990
	Rover Enthusiast Magazine James Taylor November 2007