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).
Engine performance gains from a high compression head and comparing different car models.
| Identifier | ExFiles\Box 82\3\ scan0244 | |
| Date | 7th May 1935 | |
| -2- Now we claim 15 to 20 HP. from the high compression head, and the average of your results, cut-out closed and open, is a gain in top speed of 2.75 m.p.h. which is just about what we expect. The reason one gets such a small increase in speed from such a large increase in horse power is that the power to drive the car increases as the square of the speed, and that to do 100 m.p.h. on the standard Bentley, about 170 HP. would be required. We send you wind resistance curves which demonstrate this. The main benefit conferred by the high compression head is improved acceleration. We cannot believe that if your car and Sr's car were loaded up to the same weight that there was no difference in acceleration. Of course if they were not loaded up to the same weight we know that 2 cwts. on the car would balance the high compression head. The acceleration figures which you sent through at the beginning of the test are better than anything you have previously obtained, in spite of the weight of the car. Finally, in your report on 4-B-IV of the 1st August last you said that when you had adjusted the crankshaft damper the engine was smoother throughout the range, and detonations although reported were not such as would be objected to, and could be cut out by judicious use of the ignition lever. The head you have got on 5-B-IV is the same head as that which was fitted to 4-B-IV, the only alteration being larger inlet valves, so that it is another example that one obtains different impressions under different conditions. Regarding the controllability of the car, the high centre of gravity of the body doubtless accentuates the difficulties, but we shall shortly have the single point mounted wings and radiator fitted up with the standard body, and then shall be able to formulate impressions as to the actual effect. How do you think Sr's bodies in Paris are standing up with the bumper bar, compared with 5-B-IV? Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||