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).
Comparison of different ignition coils, including bakelite, staballite and Goshawk types.
| Identifier | ExFiles\Box 45\4\ Scan122 | |
| Date | 14th December 1922 | |
| Contd. -3- EFC2/T14.12.22. position. The experimentally instructed coil with increased size of core and absence of hedgehoggings is not yet ready for test but further comparative tests have been made between the improved bakelite coil with longer (but not larger) core, four-layer primary and air space between secondary and case, and the standard 40/50 coil, and we attach a copy of a report of such a comparison on the car by Mr. Lidsey, from which it will be seen that though the 40/50 coil is generally rather better, nevertheless the other coil of lower inductance is more satisfactory at the higher speeds, which would be expected. Another similar bakelite coil with longer core has been investigated by the Test Dept. and they report that under working conditions i.e. without an additional external spark gap, the coil has never actually failed though they do not feel that it provides quite as much margin against failure as the 40/50 stabalite coil. A comparison of the wheelcase position with the engine position on different coils tried on the chassis is as follows :- Slow speed, running light, after one hour's run in each case with engine water temperature from 90 - 100°C. The figures given are the maximum allowable external spark gap just not to produce missing fire. Previous standard Goshawk coil on cyl.head - nil. " " " " Bracket - .030" | ||