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 report comparing the performance of various spark plugs.
| Identifier | ExFiles\Box 49\5\ Scan198 | |
| Date | 9th February 1921 | |
| -2- HS {Lord Ernest Hives - Chair} 5/LG9.2.21. Type of plug. | No. tested. | Test 1. | Test 2. | Test 3. | Test 4. | Test 5. | Remarks. ---|---|---|---|---|---|---|--- Bethlehem U.S.A. | 12 | O.K. | O.K. | O.K. | failed. | O.K. | 4 porcelain cracked. Splitdorf E.148. | 6 | O.K. | O.K. | 3 failed. | | | Mica insulation. Mercury GB. 2-point. | 6 | O.K. | O.K. | O.K. | O.K. | O.K. | One porcelain found cracked before using. Mercury GB. 3-point. | 6 | O.K. | O.K. | O.K. | O.K. | O.K. | Very good plugs. Detachable. Heath. | 4 | O.K. | failed | failed. | o | | Cooke 4-point. | 18 | O.K. | O.K. | O.K. | failed. | O.K. | Cannot be cleaned. Forward. | 6 | O.K. | failed. | | | | Bosch German. | 6 | O.K. | O.K. | 2 failed. | | | Cannot be cleaned. Lodge 19.G prcelain. | 6 | O.K. | O.K. | failed. | | | Missed fire badly. Hertz 2-point. | 6 | O.K. | failed. | failed. 2. | | | Mica insulation. Hertz. | 6 | O.K. | failed | failed. | | | Mica insulation - cannot be cleaned. Equem. | 6 | O.K. | O.K. | failed. | | | Misfiring badly. Champion U.S.A | 6 | O.K. | O.K. | O.K. | O.K. | leak. | * * * | 6 | O.K. | O.K. | 1 failed. | O.K. | O.K. | Goshawk car. * * * | 6 | O.K. | failed. | | | | On test car. Fan Flame. | 6 | O.K. | failed. | | | | Missing slightly. Appollo. | 6 | O.K. | failed. | failed. | | | | ||