From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Modifications to improve the Bensport engine's power output for a saloon car.
| Identifier | ExFiles\Box 3\4\ 04-page156 | |
| Date | 11th January 1933 | |
| To R.{Sir Henry Royce} From Ha/Rs.{Sir Henry Royce's Secretary} F to SS.{S. Smith} Nor. c to A.{Mr Adams} AV. c.to DA.{Bernard Day - Chassis Design} Hdy.{William Hardy} Ha/Rs.{Sir Henry Royce's Secretary}1/AT.11.1.33. BENSPORT POWER OUTPUT. The specification for the saloon car was that it should have a lap speed on Brooklands of as near 90 m.p.h. as possible. Originally the J.I. engine power curve peaked at just below 4000 r.p.m. curve N4.B (1). This meant that to do 90 m.p.h. the car had to be geared rather more than 10% higher than the existing 20/25. From the point of view of acceleration this was somewhat undesirable, as it is apparent that the weight of the Bensport car will be over 30 cwt. when it is completed. Our object, therefore, was to put the peak of the power curve up to 4500 r.p.m. and so maintain maximum low speed pick up. The mechanical side of the unit presented no difficulties. The valve gear fitted up as on 16.G.IV while at W.W. runs up to 4700 r.p.m. before bouncing begins. The crankshaft, which had journal bearings 1/8" larger diameter than existing 25 HP. standard, reaches the fringe of its critical speed at 4400 with the Chrysler system of balance weights, but with the 6/8 wt. scheme this will be raised to 4500. The light flywheel having little overhang would probably permit of a small reduction in the balance weights to raise still further the critical speed, if this was found desirable. The existing single contact breaker distributor is not satisfactory above 4000 r.p.m. For experimental running, the double contact breaker has been adapted to the existing crankcase. The propeller shaft ceases to be a problem with the separate gearbox construction. The first step in improving the high speed power was a longer duration camshaft, which R.{Sir Henry Royce} produced, which increased the inlet duration some 20°. This camshaft | ||