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).
Bench tests and modifications for improved performance on a 25 HP engine.
| Identifier | ExFiles\Box 181\M9\ img009 | |
| Date | 5th August 1931 | |
| SPEED FILE 12 GIV ORIGINAL To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} c. Sg.{Arthur F. Sidgreaves - MD} c. Wor.{Arthur Wormald - General Works Manager} c. E.{Mr Elliott - Chief Engineer} c. Da.{Bernard Day - Chassis Design} EV.{Ivan Evernden - coachwork} Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}3/AD.5.8.31. X5771. 85770. IMPROVED PERFORMANCE 25 H.P. We carried out some bench tests to see how much we could increase the power output of 'China' without increasing the compression ratio excessively or spoiling the low speed pick up, with a view to satisfying such people as Lord Cholmondeley. The modifications or departures from standard carried out on the power unit were :- (1) 112° W.W. camshaft. (2) Valve lift increased .050 (3) Compression ratio 5.6 - 1 (4) Stronger contact breaker spring. (5) Stronger valve springs. (6) Increased output coil to give even firing under full throttle low speed. (7) Increased range of automatic ignition advance. A feature that we considered desirable but did not fit, were stiffer push rods. The power obtained from this unit with the standard and with an S.U. carb. is shown on curve Rm.{William Robotham - Chief Engineer}27. The depression of the S.U. is very low. A Solex we have been running with the same throttle dia. (1 1/8") gives nearly 1" higher depression at 3000 R.P.M. with a less satisfactory pick up though we have not yet made a road test of its petrol consumption. We have fitted the improved unit to 12-GIV having previously obtained speed figures for this car in a standard condition. In addition to changing the engine we changed the exhaust system by fitting a Phantom II type silencer and fish tail. The effect of changing the exhaust system is shown in Rm.{William Robotham - Chief Engineer}26. It will be observed that the W.W. scheme to N.Sch.3286 gives much the same results as the P.II system and we should have used it had it not been fitted to another car at the time. Either system results in a gain of 7 - 8 H.P. over standard. | ||