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).
Page detailing carburetter performance, specifically comparing the Phantom carburetter to static carburetters like the Twin Solex.
| Identifier | WestWitteringFiles\T\2January1929-June1929\ Scan078 | |
| Date | 28th January 1929 guessed | |
| contd :- -6- that the latter carburetter has an air valve lifted by the engine suction should not appreciably slow down the acceleration of the car providing the damping of this valve is not excessive because the air valve is capable of responding to, or following, the increase of engine speed at a much greater rate than is permitted due to the mass of the car. In cases where the acceleration has been found better with static carburetters than with our own - for example the Twin Solex on the Phantom - can only be due to the greater low speed torque resulting from the former. The Phantom carburetter operates at a high depression and this cannot be appreciably reduced without losing certain other qualities. It may be explained as follows :- The low speed choke has to be kept small to cater for the lowest engine speed. A plain jet is used in this choke, which requires compensating air to keep the mixture ratio constant. The compensating air admitted through the high speed choke via the air valve diaphragm and it is necessary to control the air valve by a comparatively stiff spring to avoid too much air dilution. This means that the depression increases rapidly with the air consumption. Further an appreciably high depression is reached in the carb. before the air velocity in the high speed choke - low speed compensating air - is sufficient to raise fuel from the main jet. The high depression in the carb. body is not felt in the high speed choke and therefore does not help the high speed jet to supply. Further, the mixing chamber is not of a form which assists in the restoration of pressure. contd :- | ||