8-Litres, and blown too!
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Considerable interest was aroused by the appearance at the VSCC Oulton Park and Silverstone Race Meetings of RJ Cooper’s supercharged 1930 8-litre Bentley, the first blown version of this famous car. It started life as a long-chassis saloon, which Mr. Cooper delivered on a lorry to the well-known Bentley specialists, Hofmann & Burton, of Henley-on-Thames, when it was badly in need of restoration. It was then converted into the present delectable sports model by first thoroughly overhauling it and then, following out an almost chance remark by George Burton, supercharging it. The compression-ratio was raised to 61/2 to 1 with new Martlet pistons and special valves, based on those evolved from the BDC high-speed tests at Monza, installed. Otherwise the engine is absolutely standard. The supercharger, on the off side of the engine, is a big Wade, like those used on Commer diesel engines, sucking from two 2-in SU carburetters. It is driven from the nose of the crankshaft by a North British Rubber toothed belt triangulated over a third pulley which drives, through a jack-shaft to spare the armature, a Lucas dynamo, the original dynamo between the front dumb-iron having been removed. The blower pressure is approximately 4 lb/sq in, and with the wheels in use at Oulton Park Burton reached a maximum engine speed of 3.800 rpm, which gives 120 mph on the speciallycut 3-to-1 axle ratio. A Speed Six differential assembly is used to reduce the angle of the transmission line.
The Bentley has a shapely sports body built by Hofmann & Burton of tubular steel covered in 20 g aluminium. This body weighs only 90 lb inclusive of facia and instruments, and the entire car turns the scales at 331 cwt with four gallons of fuel.
How does this blown 8-litre behave on the road ? It has exceedingly effective torque from really low rpm, so that it does almost everything in top gear in spite of the high axle ratio, which gives a speed of better than 68 mph at a mere 2,000 rpm. The engine thrives on Esso Golden petrol and the worst consumption has been 14.2 mpg on the Oulton Park week-end, including the racing. On the road 16 mpg is not unusual. The brakes, which have been hydraulicised, tended to overheat badly under racing conditions but Alfin drums have effected a great improvement. In this 8-litre Bentley Mr Cooper has a potent and unique motor car.—WB.