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).
Comparative test report on engine modifications including larger diameter valves, different carburettors, and higher compression ratios.
| Identifier | ExFiles\Box 5a\5\ 05-page034 | |
| Date | 1st April 1927 guessed | |
| contd :- -2- ation in this direction. We considered that the larger diameter valves, in order to make a true comparison with those of the std. dimensions, should be tested in conjunction with carbs. giving a low induction pipe depression, as an undersize carburetter could entirely mask any advantage possessed by and expected from the resulting greater valve inlet area. Comparative tests were therefore made on the test bench with the larger and standard valves and the two Zenith triple diffuser carburetters belonging to the Lorraine. These carburetters were approx. the correct size for the 20 HP., there being little difference in the capacities and speeds of the two engines. A compression ratio of 5.4 to 1 was employed for all the tests. The only reason for using a ratio higher than the standard 4.75 to 1 being that the test engine available was already fitted with the higher ratio pistons. Short free exhaust pipes fitted to each of the three ports were employed to avoid any discounting of the results which might occur due to a probable increase of back pressure with higher volumetric efficiency. A single and two Zenith carburetters were tested against the standard RR. carb. and arranged as shown on an appended print. With the two carburetters - each feeding three cylinders - no balance pipe was employed. There was no petrol blow back with the carburetter intake covers fitted. contd :- | ||