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).
Special ignition coil tests and requesting optimal ignition advance settings for various engine speeds.
| Identifier | ExFiles\Box 37\1\ scan 216 | |
| Date | 20th April 1920 | |
| X 3949 To EFC. from R.{Sir Henry Royce} Copy to CJ. " Bn.{W.O. Bentley / Mr Barrington} " Hs.{Lord Ernest Hives - Chair} R3/G20.4.20. RE SPECIAL IGNITION COILS - X.3775.EFC2/T13.4.20. X.3949. I read the result of your tests of the coil with much interest. You will remember that I was asking you to test if we can get equally good slow running with shorter spark gaps and a smaller number of larger gauged wire on the secondary coil, and so work with less high potential. Apparently the coil E.12 would demonstrate this point. The other point was whether a coil having more insulation and less wire could be used if the insulation was better. I quite agree that the only place to judge the efficiency of the coil to fire the engine will be on the car. Working under the present arrangement, even with a coil near the distributor, there does not appear to be much possibility of using less than 14,000 turns in the secondary winding. I think your tests are very consistent. I am now anxious to learn from Mr. Hives what he considers the best advance (after starting from a retarded position) for various speeds, i.e. (1) What is a retarded position which is sufficiently safe to prevent any risk of back firing. (2) The advanced position for the slowest speed of engine that we are likely to require, such as very hard pulling say, 500 revs. then the extra advance necessary from 500 to 1000, and 1000 to 2000, 2000 to 3000. Perhaps you could help to get this information recorded, preferably for an engine like the "Hawk" and our present car engine. This information is wanted for automatic advance. R | ||