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).
Graphs comparing engine fuel consumption efficiency with one versus two spark plugs under different loads.
| Identifier | ExFiles\Box 69\4\ scan0326 | |
| Date | 5th October 1926 | |
| Top Graph: △ TWO PLUGS SYNCHRONISED. ◉ ONE PLUG. CARB. SIDE OF ENGINE. LIGHTER PHANTOM ENGINE. SPECIFIC CONSUMPTION WITH ONE & TWO IGNITIONS. 4.69 TO 1 COMP. RATIO. CURVE SHEWS NO APPRECIABLE DIFFERENCE IN EFFICIENCY WITH ONE OR TWO PLUGS. 1250 R.P.M. FULL LOAD. Y-Axis: PINTS/B.H.P./HOUR. X-Axis: B.M.E.P. Bottom Graph: EFFECT OF IGNITION ON EFFCY WHEN THROTTLED. ◉ ONE PLUG AT 35° ADVANCE. △ SYNCHRONISED IGN. AT 27° ADV. 1000 R.P.M. SYN IGN ADJ TO GIVE MAX TORQUE FOR EACH LOAD. CURVE SHEWS THAT NO APPRECIABLE DIFFCE EXISTS BETWEEN ONE OR TWO IGNS. UNDER LIGHT LOADS. Y-Axis: PTS/B.H.P./HR. X-Axis: %AGE OF FULL LOAD. Bottom Right Corner: ACF 5/10/26 | ||