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).
Sparking plug voltage tests carried out on various chassis.
| Identifier | Morton\M13.2\ img011 | |
| Date | 7th December 1930 | |
| EECL/ADL7.12.30 contd. -2- The sparking plug voltage tests were carried out on both a 20/25 and 40/50 chassis and the maximum sparking plug voltages under the worst conditions of acceleration from 10 to 25 miles per hour on top gear, with full throttle and fully retarded ignition, were noted. In the words of my assistant's report :- "This voltage was measured by using our calibrated sphere gap voltmeter which was shunted across each sparking plug in turn and so adjusted in each case as to spark over when the absolute maximum voltage condition was reached. Several trials were made with each plug in order to get the maximum voltage. This procedure was carried out with standard Lodge type C plugs on experimental Phantom II chassis 19-EX with standard compression ratio 4.6 to 1 and with the sparking plug gaps set at .025" and at .030" (.025" standard setting), also with standard K.L.G. type K.1 plugs on a production 20/25 chassis from the Test Dept. compression ratio 5.25 to 1, in this instance with the plug gaps set at .020" and at .030" (.020" standard setting). The engine cooling water temperature in each case was maintained at approximately 70°C. but in the case of chassis 19-EX an additional test was made with the plugs very hot, the engine being warmed up by allowing the cooling water temperature to be maintained at boiling point for half an hour. The results obtained are set out as follows:- Phantom II chassis 19-EX. (a) Plug gaps .025" water temperature 70°C. Cylinder No. Plug voltage. 1 4820 2 5050 3 6300 4 7800 5 6200 6 5920 Average maximum voltage per plug 6015. | ||