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).
Pre-ignition issues caused by mutual induction between the battery and magneto ignition systems.
| Identifier | ExFiles\Box 163\7\ img017 | |
| Date | 11th April 1921 | |
| XH284 b To FFC. from R COPY c. to CJ. c. to HS.{Lord Ernest Hives - Chair} R9/G11.4.21. X3199 RE BATTERY IGNITION. X918 X4284 X3199 X3445 It has occurred to me that the reason we get pre-ignitions by mutual induction is because we have double ignition and in certain control positions the battery is much retarded relative to the magneto, hence the battery ignition is trying to fire a charge already exploded. Delco as applied to cars we have seen has not this disadvantage, and hence can have wiring which we think is arranged so as to have this trouble. They probably have never experienced it, and we should not get it if we switched off magneto and used battery only. A safety gap on coil might also prevent it, or a coil having only the exact length of spark needed i.e. the 8 mm. in air at atmospheric pressure. R.{Sir Henry Royce} | ||