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).
Comparing the performance of a new coil versus an old coil with varying plug gaps.
| Identifier | ExFiles\Box 178\4\ img013 | |
| Date | 4th April 1932 | |
| A.{Mr Adams} From HS{Lord Ernest Hives - Chair}/Hst. c. to Sy. c. to Ss.{S. Smith} H.T. c. to M.{Mr Moon / Mr Moore} IGNITION APPARATUS PLUG AND SPARKING VOLTAGE We thank you for your E.1/M.2.4.32., with reference to the above. Before we standardized our new coil we made a prolonged series of tests on the chassis and on the bench with the old coil and the new one also with varying plug gaps. With the old coil we could not run a A/25 on load for any length with plug gaps more than .020". With our new coil we could run quite satisfactorily with the coil quite hot with .030" plug gaps. These tests were also confirmed by Mr. Hancock on 16.H.IV. during the last 10,000 mile test. We have carefully observed the distributor (with windows cut in) for sparking over but have not observed, at the time when misfiring was occurring, any jumping over at this point although we are of the opinion that our present distributor insulation distances are very small. K.E.G. therefore is much better in this respect. With the aid of an improvised sphere gap voltmeter we have observed that the plug voltage rises to very high values when "picking up" from dead slow under load. We were able to see that these voltages were in excess of the maximum regular sparking voltage given by the old coil. We do feel therefore that our new coil is a definite improvement. With regard to plug gaps we think you will agree that the smaller we keep them the less the likelihood of good slow running. This has been demonstrated by other people and K.L.G's definitely say that below .025" plug gap slow running becomes worse. American cars usually have their plugs set from .028" to .035". | ||