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).
Guide on the properties and usage of 'Racing Shell' fuel for various engine types.
| Identifier | ExFiles\Box 20\4\ Scan050 | |
| Date | 18th February 1930 guessed | |
| "Racing Shell" is obviously a better fuel than pure benzol, or any mixture of benzol and petrol; it is far superior, of course, to standard mixtures. Its anti-knocking effect is similar to that of pure benzol—it has, however, satisfactory starting properties, and is not “sluggish” in acceleration. Some years ago the requirements of the somewhat less efficient “hotted-up” engine of those days were met by the 50-50 petrol/benzol mixtures then sold. To-day “Shell” has a definite superiority in anti-knock value (as well, of course, as in other respects) compared with the weaker benzol mixtures now ordinarily sold; but in the case of the abnormally “hotted-up” engine, generally where a supercharger is employed, it is admitted that even “Shell” is not ideal for maximum performance in these abnormal engines, although it is the best motor fuel sold at present for all normal purposes. “Racing Shell” (designed, as stated above, for a special need) is intended for use neat, or admixed in any suitable proportion with “Shell,” to meet the individual needs of “Super Sports” or racing cars. This super spirit now becomes available for all extra high compression engines, and “Shell” remains the ideal fuel for all normal types. How to use “Racing Shell.” Pour in the “Racing Shell” after the straight Shell. “Racing Shell” gives the best results if mixed with “Shell” in just the correct proportions to satisfy the engine’s compression ratio. Engines, even of similar design and capacity, vary in their knocking characteristics, and it is not practical to set up an arbitrary table of proportions covering all cars. For Sports Types. The correct proportions are best determined by experiment and as a general rule, owners of sports types should commence with a mixture of 10% “Racing Shell” and 90% Shell—then, if the engine still tends to knock, the proportion of “Racing Shell” should be gradually increased to the point where knocking is eliminated on full throttle with full spark advance and with the engine running fast enough to drive the car comfortably in any gear. For Superchargers. If a supercharger is employed the engine must be run fast enough to ensure that the supercharger is working effectively. For Racing Cars or Motor Cycles. For racing cars a 50/50 mixture of “Racing Shell” and “Shell” should be tried out first, and the proportions of the former increased or diminished to the point where detonation (or knocking) is just eliminated on full throttle, with full spark advance and at engine speeds of approximately over 1,500 r.p.m. If a high degree of supercharge is employed it may be necessary to use 100% “Racing Shell.” There is no advantage in using a greater percentage of “Racing Shell” than that required to eliminate detonation, and in seeking the correct proportion it is best not to fill tanks to capacity, but to commence, for example, if trying out a 20%-80% mixture, with one gallon of “Racing Shell” and four gallons of ordinary Shell, this being sufficient for a try-out, and permitting, if the contents of the tank can be measured, further experiments in proportions without unduly protracted running. Whilst the anti-knocking effect of “Racing Shell” may permit a further degree of spark advance, it must be remem- | ||