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).
Analysis of Wraith engine characteristics, comparing its performance with a Humber 'Super Snipe' and evaluating different camshaft and induction systems.
| Identifier | ExFiles\Box 108\2\ scan0195 | |
| Date | 13th January 1939 | |
| 600 By.{R.W. Bailey - Chief Engineer} from Rm.{William Robotham - Chief Engineer} c. Da.{Bernard Day - Chassis Design} c. Da{Bernard Day - Chassis Design}/Jnr.{Charles L. Jenner} c. Rm{William Robotham - Chief Engineer}/Wym.{G. Harold Whyman - Experimental Manager} c. Rm{William Robotham - Chief Engineer}/GR.{George Ratcliffe} WRAITH ENGINE CHARACTERISTICS. We got a shock the other day when we put the Humber 'Super Snipe' on the dynamometer, and found out what an excellent horse-power it had under 'all on' conditions. We attach a curve showing the horse-power of this unit compared with that of the Wraith, together with other particulars. We admit that we have first and foremost endeavoured to make the Wraith a silent and smooth motor-car. On the other hand, the Humber 'Super Snipe' is also silent and sweet. Therefore, by development we ought to be able to improve the performance of the Wraith without detracting from its pleasant characteristics. Tm/CTS.{C. Trot Salt - Carburation} has done an analysis showing the effect of different camshafts and induction systems on power output. Incidentally, this included a camshaft which gave us a new firing order, but this was definitely less satisfactory than our existing arrangement. The power curves confirm the fact which we proved a little while ago, that the Bentley Induction System gives a considerably better power output than the Stromberg. We know that two carburetters can give a better maximum torque than a single, but given equal induction depressions, have never found that there was any difference in top horse-power between two and one carburetter. Therefore, the difficiencies of the Stromberg Carburetter and Induction System at high speeds wants investigating, particularly when used with a high output camshaft as on S.67. The state of affairs with regard to the camshaft is interesting. We went to extreme of short duration in order to get (1) good idling (2) maximum low speed torque. It now appears that we cannot use the low speed torque we have got without running into detonation, and have to reduce this torque by retarding the ignition on the governor characteristic. Therefore, we believe, with regard to low speed power we should be just as well off with the Bentley camshaft as with the Wraith. | ||