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).
Conclusion on factors for improving fuel economy, focusing on the vacuum control unit and ignition system.
| Identifier | ExFiles\Box 163\7\ img339 | |
| Date | 30th June 1939 | |
| -3- RM{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation}19/JH.30.6.39. strength of this spring is therefore in proportion to the size of the diaphragm. It is suggested that RM{William Robotham - Chief Engineer}/RC.{R. Childs} should obtain a unit from Lucas having a diaphragm area increased by at least 50% with correspondingly stronger spring fitted. This will undoubtedly be the avenue of approach on future development of the Vacuum control unit. Conclusion. Considering all the factors contributing to improved fuel economy, the following points are outstanding. (a) The factors have to be effectively combined to provide a satisfactory result. For instance, it is useless to just fit a suction advance unit to a car and expect to get much improvement in fuel economy. Wider plug gaps (or long reach plugs) should be combined with this move. It should then be possible to use a weaker carburetter setting, but only for part throttle, the full throttle mixture strength should be maintained as before. (b) As stated previously, Vauxhalls now believe that their ignition system is the main limiting factor to improved fuel economy. We have better grounds than they had for believing that the same is true of our own product. The best example is the latest Rolls-Royce semi-developed ignition distributor. (c) We have never seriously tackled this ignition problem. Eighteen months ago we obtained a Lucas Peak Voltmeter for determining the required ignition voltage for firing lean mixtures (as per Vauxhall). We have had little chance to use it because there are hardly two ignition systems which do their work the same. To prove this from a production standpoint - Sir James Wilsons' car was recently fitted with raised crown pistons raising his compression by a complete ratio. The performance was improved considerably but detonation was no worse than standard. We know from our own tests, that there is only one answer to this, the ignition governor was lagging behind at low speeds. | ||