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).
Ignition system development, including spark plug findings, vacuum advance, and petrol consumption.
| Identifier | ExFiles\Box 163\7\ img338 | |
| Date | 30th June 1939 | |
| -2- Distribution. They still use the spark plug temperature method by use of thermo-couples, and we will have to take their word for being able to obtain consistant results. Ignition. This is the feature on which they are now concentrating their energies. In other words, Taub is trying to get Lucas to bring their ignition system up to scratch. They have been supplied with an engine, complete with flowmeter and required consumption figures. One of their more recent findings, is the fact that a long reach plug with points away from the combustion chamber walls, gives the same effect as wide plug gaps, but with better results. The actual value of this move is dependant on the scavenging characteristics of the particular combustion chamber. They claim 3 m.p.g. improvement on the road. Vacuum Ignition advance. There is no doubt that between 10 - 20% improvement in petrol consumption will result from the use of vacuum controlled ignition advance for part throttle running. The actual gain is dependant on how much extra advance one is able to use, and Vauxhalls cannot use the maximum desireable amount for the same reason that we have been unable to use it at all. The explanation is as follows. Low speed detonation and engine roughness is seriously affected by the 'lag' in operation of the suction unit. Imagine that one is touring on the road in top gear at 15 m.p.h. At this speed an extra 25° ignition advance could be used with advantage to part throttle economy, but on snapping the throttle open for get away, the vacuum unit does not return the spark position to normal with the same rapidity; so that momentarily the ignition is over advanced for the full throttle condition. The amount of useable suction advance, is therefore dependant on the amount of lag. It is interesting to consider the controlling factor in the unit, which is the spring. This spring is required to overcome suction on the diaphram at full throttle, but the | ||