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).
Alterations to ignition timing for the 25/30 HP engine to improve slow speed running.
| Identifier | ExFiles\Box 163\7\ img312 | |
| Date | 10th June 1937 | |
| WST 6013 By: Copy to Farr Rm{William Robotham - Chief Engineer}/Wst. E/JNR.{Charles L. Jenner}1/M.10.6.37. Re: 25/30 HP. SLOW SPEED RUNNING. We re-issue to you LeC.5691. The alterations that have been made to the original drawing are the direction of operation of the spring and the cam form. The features of this scheme are as follows:- (1) With the foot off the accelerator pedal, ignition is retarded 10° from normal (or other amount as decided upon when designing the cam). This means (a) ignition is sufficiently retarded to prevent back-firing when starting the engine. (b) ignition is sufficiently retarded to smooth out the roughness which becomes apparent in a flexibly mounted engine running at idling speeds (as when held up in traffic). Neither of the above functions can be performed by a vacuum control unit, in fact under certain circumstances the vacuum unit would alter the ignition in the reverse direction to that which is desired. (2) When the accelerator pedal is depressed 1/4 of its stroke, the cam advances the ignition 10° (or other suitable amount) beyond the normal setting. When the accelerator pedal is fully depressed the ignition is returned by the cam to its normal setting. Between these two positions (1/4 depressed to fully depressed) the ignition is advanced a proportionate amount. This provides the extra ignition advance which is necessary to obtain the best output from an engine | ||