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 engine roughness, fuel compatibility, compression ratio, and tyre performance for the Big Bore Bentley.
| Identifier | ExFiles\Box 83\4\ scan0001 | |
| Date | 18th October 1935 | |
| G.W. Hancock, Esq., Hotel de France, Chateauroux, Indre, France. +200a Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}1/KW.18.10.35. Big Bore Bentley. We are anxious that the big bore Bentley engine shall be as smooth as the present standard Bentley. I myself was very disappointed with the roughness of the car when it was in England, but thought it had improved after Hives' run. It has always been much rougher than the same unit in B-1 car, which makes me suspect that the engine mounting is somewhere at fault. Actually I felt that the engine was somewhere making contact with the chassis; i.e., either the floorboards, front engine mounting, exhaust system, dashboard or somewhere, but you will doubtless report on this. I do not mind the detonations on standard petrol. If the Bentley is to hold its position as a Sports Car, the customers have got to use the best petrol that is universally obtainable. You cannot feed a racehorse on bran. Actually the French Esso, as I have previously pointed out, is only 76 octane and the English Esso is 80, so that we should expect slight detonations on the French leaded fuels. Banks expects that these will shortly be brought up to 80 octane in France. As you know, this unit is 6.8 compression ratio, which is a compromise between the present standard and the high compression head. With a view to giving you an opportunity of seeing what lowering the compression ratio will do in making the engine smoother, we are sending out a liner to be put under the block. We should like your opinion on whether this improves the motor car or not. Regarding the tyres, if you like the India Super Aero Cushion we shall be glad to know, and we will send you some more. Our opinion is that at 28 lbs. tyre pressure they are more comfortable than the standard India tyres and give reasonably good road holding. The tyre pressures are very important and you may find that some other figure is more suited to your running. | ||