Comparison of the S.U. manufacturer's recommended settings for a starting device versus Rolls-Royce's own method.
| Identifier | ExFiles\Box 122\4\ scan0221 | |
| Date | 21th March 1939 guessed | |
| -2- The initial setting of the S.U. starting device is a most important point, because its performance depends to such a large extent upon the method of setting adopted. The makers do not pretend that the device is anything more than a compromise, but they do recommend a method of initial setting which gives the best compromise. This is as follows:- First it is necessary to know the cutting out temperature of the device. The engine is then run at this temperature with the device "in". The starter carb. is then set to give a mixture as rich as the engine can take; actually on the point of hunting. This setting gives an instantaneous start at 0°C. Our method of setting has been as follows:- The starter carb. is set to give a mixture just rich enough to start and maintain running at -7°C. At this temperature the engine is running at 500 r.p.m. and the speed increases as the engine gets warm, so that when the starter carb. cuts out the speed is 1000 r.p.m. (if no freezing up takes place). At the cutting out temperature running at this speed, firing is quite even. We consider, however, that this setting is in itself a compromise, because we say that to adequately cover the cold starting question so that our cars start instantly under all conditions, the carburetter has to be set rich enough to just start and maintain running at -14°C. On the S.U. starter, when the engine has warmed up and the cutting out temp. reached, running is uneven due to over rich mixture, and due to the mixture strength the speed is only 500 r.p.m. Trying to cater for these conditions we have run into the freezing up trouble, which is aggravated by the richer mixture, and in turn the effect is made worse by the lower engine speed. So we see the difference between the S.U. method and our own of initial setting. | ||
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).