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).
Carburetter modifications for increased power output compared to the 40/50 HP model.
| Identifier | WestWitteringFiles\M\2Jan1925-March1925\ Scan26 | |
| Date | 25th September 1924 | |
| R.R. 493A (50H) (D.B. 175 25-9-24) J.H.D. EXPERIMENTAL REPORT. -5- Expl. No. REF: Ha/ACL/LGTD.1.25. we have to supply a greater weight of charge per unit time than we do in the 40/50 HP. To accomplish this a larger high speed throat is used which from its fundamental characteristic operates at a lower depression over its complete range and fulfils the conditions for the greater power output. The trouble is not here, but occurs during Phase 1. On this carburetter, we retain the same size low speed throat as in the 40/50 HP. (viz. - .1600 dia.), and larger diaphragm ports in the high speed throat. Therefore, with this size of throat, in order to maintain a constant quality of mixture over this phase, we shall have to work at the same depression as in the 40/50 HP. That means that in order to work at the same depression we must use even a stiffer (higher rated) spring than is employed in the 40/50 to allow for the larger effective area of the air valve piston and the larger diaphragm ports, but actually, we are using a lower rated spring and larger diaphragm ports. If, however, the low speed throat were enlarged in the correct proportion, the metering would again be equal to the 40/50 HP. and the carburetter would be operating at a lower depression. The objection to the use of a larger low speed throat is that it impairs our slow running. It would seem that in order for the carburetter to work correctly at the lower depression necessary to take full advantage of the greater vol. effcy. of the EAC. engine, contd :- | ||