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).
Technical discussion on the design and function of fully automatic carburation systems and starting devices.
| Identifier | ExFiles\Box 121\4\ scan0161 | |
| Date | 25th January 1938 | |
| -2- can be corrected, before mixture reaches the main bore of the induction pipe. Quite by coincidence they have found that the most successful design of mixing chamber is to offset the throttle bore of the carburetter from the centre line of the main pipe, and take out the resultant swirl by fitting a baffle. This is the same as the latest Phantom III pipe, and is being tried on the Wraith. Fully Automatic Carburation. Before referring to the S.U. Automatic Starting device in detail, it is as well to consider what our "Ideal" demands would be when referring to "Automatic carburation", and then to see how far the S.U. device can go, towards this end. The "Ideal" is soon settled when we say that in a fully automatic carburetter, the jets should supply the correct quantity of petrol for all varying conditions of gas velocity, air intake temperature and temperature of the metal surfaces affecting the mixture on its path to the combustion chamber. In practice, the driver of the car should be unaware of any difference between a hot or cold engine, and from his point of view there should be no such thing. The nearest we have come to this condition, was the thermostatically controlled jet of the S.U. carburetter, the thermostat being subject to variations of induction pipe depression as affected by throttle position and engine speed. The latest S.U. automatic starting device does the same work as the starting carburetter fitted to the Phantom II and 20/25 engine, except that it turns itself off automatically at a certain water temperature. It has certain undesirable features, such as the same noise as our old starter carb. While the device is in action, the engine speed will not be much lower than 1000 R.P.M., and at this speed the engine is given a set mixture strength until the predetermined water temperature is reached, at which stage the thermostat causes the starter carb. to be switched out with a snap. This sudden cutting out of the starter carb, causes rather a sudden contrast against the normal carburetter setting, while the water temperature is still low; so that practically all the people who have tried it have demanded that it should cut out at a higher water temperature. If the setting is altered so that this takes place, one approaches the danger stage of not starting troubles. | ||