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).
Comparison of the Delco-Remy distributor against the standard R.R. unit for ignition performance on the Wraith model.
| Identifier | ExFiles\Box 168a\4\ img149 | |
| Date | 12th February 1940 | |
| to Rm{William Robotham - Chief Engineer}/RR To Ev.{Ivan Evernden - coachwork} Copy to Jnr.{Charles L. Jenner} Rm{William Robotham - Chief Engineer}/RC.{R. Childs}9/ML.12.2.40. Re Ignition. It is now generally agreed that the Delco-Remy distributor gives electrically a better performance on the "Wraith" than the standard R.R. unit to DW 426. The main reason for this is in the contact breaker, which, in the case of the Delco is of the double lever type, working in conjunction with a three lobed cam: with this type a make ratio of .75 easily obtainable. The R.R. unit has a single lever breaker and works in conjunction with a six lobed cam: with this type it is not practical to obtain a make ratio of more than .55. The attached curves show what this means with regard to coil output. Comparing the respective "Current at break" curves we note that the double lever breaker gives an increasingly greater value, for all speeds over about 15 m.p.h. and as these curves are directly proportional to the coil output the available energy at the sparking plug will also be greater. Below 15 m.p.h. the double lever has no advantage over the single lever. We know from past experience that poor running is caused by weak mixtures affecting the plug electrodes in such a way as to raise the firing voltage and that if this extra voltage is not available either a miss or a weak spark ensues. In the latter case, even if the mixture is fired, lack of energy may cause delayed firing with a consequent loss of power. Although the advantage gained at speeds of 15 - 25 m.p.h. is small it is logical to assume that the greater dissipation of energy at the plug electrodes during the higher speeds will tend to keep them clean and in this way help to improve slow running. Since we already have at our disposal the best coils on the market we must make certain that they work under the most favourable conditions; for this reason we have specified the standard B60 Delco-Remy distributor for the Ripplet 2 - R -ii and have arranged for the positive terminal of the battery to be earthed. | ||