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).
Test results for sparking plug voltages on a 20/25 HP chassis at different plug gaps.
| Identifier | ExFiles\Box 37\1\ scan 188 | |
| Date | 5th December 1930 guessed | |
| (4) very hot there is a voltage reduction of about 15%. 20/25 HP Chassis. a) Plug gaps .020" Water temp. 70°C Cylinder No. Plug voltage 1 5920 2 6020 3 7200 4 6600 5 6300 6 5920 Average max. voltage per plug. 6330 b) Plug gaps .030" Water temp. 70°C Cylinder NO. Plug voltage 1 8500 2 9700 3 9200 4 9700 5 7550 6 7550 Average max. voltage per plug 8870 ✓ These tests indicate very clearly, abnormal sparking plug voltages due to severe ignition conditions on the 20/25 HP chassis particularly when the plug points oxidize and the gap increases slightly due to erosion etc as is almost invariably the case after a short mileage. We consider and would recommend that .030" | ||