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).
Letter discussing the performance of high compression cylinder heads, engine roughness, and the effect of petrol quality.
| Identifier | ExFiles\Box 82\3\ scan0243 | |
| Date | 7th May 1935 | |
| To G.W. Hancock, Esq., Hotel de France, Chateauroux, Indre, France. X200A Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}18/KW.7.5.35. Many thanks for your notes re high compression cylinder heads, etc. We appreciate that you have done a lot of work changing over road springs etc. The results are of very definite value. We should like your opinion of your engine with the standard cylinder head on. We are under the impression that it is an objectionably rough unit, even with the standard compression ratio. We think we know why this is: it is tied up with the flywheel, and we are doing some experiments to demonstrate that if we have a heavier flywheel we can improve the engine smoothness. With regard to the roughness of the high compression head, it is of course definite that it makes an engine rougher than standard. However, if we take Lappin's case, he is delighted with the results and would much prefer it to the standard. We are not saying that if he was running the car under your conditions he might not form the reverse opinion, it is merely a question of average results, particularly after the head is carboned up. Another point is that we now have petrol in England of 80 octane rating. We do find that a really good petrol makes the engine feel smoother. Possibly even with lead the French petrol is not up to 80 octane value. However, we shall have an opportunity of confirming all these results when we get a few more high compression heads about. I am not wildly enthusiastic about them myself. On the other hand, the Americans are running at 7 to 1 and we have to maintain our position in the Sports car world, which depends largely on performance. It is on the performance obtained from the high compression head that we disagree with your conclusions. The maximum speed obtained from any power improvement will always be disappointing. As an example of this, note that the horse power gained at the road wheels by opening the cut-out is 9 on the Bentley. The increase in speed is 1.6 m.p.h., the average of the two heads given in your memo of May 2nd. | ||