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 detonation issues, fuel octane ratings, and ignition timing for a Bentley.
| Identifier | ExFiles\Box 89\1\ scan0169 | |
| Date | 8th November 1935 | |
| VW201a Exptl. Dept: Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}12/KW. 8th November, 1935. R.{Sir Henry Royce} Summers, Esq., Denna Hall, Burton Point, Chester. Dear Dick, I have not got your samples calibrated yet, but in the meantime have got some figures from the Ethyl Export Co. which rather bear out the results obtained on your car. You will observe that even if Benzol mixture was composed of a good No.1 spirit with 30% Benzol added, it would still only have an octane rating of 75, or 5 points below Ethyl as at present being marketed. When the Bentley was originally put on the market it was really designed to run on Ethyl petrol as in existence at that time. You will note that this is 76 octane. I think there is no doubt that all the fuels you are running on with the exception of Ethyl are below that figure. I quite agree that the detonation which comes on round about 50 m.p.h. is undesirable, and hope to be able to modify your ignition advance to overcome this. It is possible, however, that in order to eliminate it a slight loss of power will result. The reason for this is that at 50 m.p.h. the volumetric efficiency of the engine is at its best, due to the sports type of camshaft fitted, and therefore the tendency to detonate is greatest. I hope to ring you up about your new car shortly. Yours sincerely, | ||