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).
Road test report on car 21-EX, diagnosing a high-speed petrol starvation issue caused by the autovac system, also noting high fuel consumption and steering performance.
| Identifier | ExFiles\Box 65a\3\ scan0065 | |
| Date | 4th July 1929 | |
| To Hs.{Lord Ernest Hives - Chair} From G.W.H. Hôtel de France, Châteauroux, Indre. 4/7/29. We took over 21-EX yesterday afternoon from Mr. Northey in Paris. We have returned to Châteauroux to-day. On our run down we have experienced the same trouble of petrol starvation as Mr. Northey had, and have definitely proved during the run that the starvation is due to the autovac not delivering sufficient petrol to maintain a high sustained speed. To give you details of what actually occurred will perhaps explain more clearly to you. The route from Paris to Orléans is a fast one, but as there are lots of bends in the road, one is continually luffing up, during which time it is quite evident the vacuum pump combined with the autovac delivers sufficient petrol in a few moments to maintain a high speed. The route from Orléans to Châteauroux, as you are aware, is almost dead straight, and very long sustained runs can be maintained at high speed. To-day, immediately we left Orléans and opened up reaching a speed of 80 on the speedometer, in a few minutes we were back-firing and losing speed. I determined to find out what was the cause, so again opened up to high speed, and immediately the shortage was noticeable had the petrol tap turned off, stopped the engine and stopped the car. Result:- No petrol in float chamber. I repeated this test again with the same result. Then we disconnected the exhaust pipe, from the carburettor of the vacuum pump. This was to prove whether the back-pressure of the silencer was the cause. We tried the car again and the same symptoms occurred. This proved definitely that it is not the back pressure. Then, to verify that the autovac and pump were not delivering sufficient petrol, I ran with the reserve tap turned on, which then you will understand gives you the reserve of petrol in the autovac. By doing this the shortage immediately ceased and we were able to maintain a high average speed continuously. An item which we had forcibly thrust upon us and which has a bearing in the matter is the petrol consumption for high speed work is round about 7 M.P.G. We ran out of petrol 14 miles away from Châteauroux having used 20 gallons of petrol from Paris. Therefore the extra petrol the engine has been using and the inefficient autovac explains the reason of the shortage, whereas previously we have had an efficient autovac and a considerably better petrol consumption, but we must have been very near the mark. I had a talk with Mr. Northey yesterday re the steering of the car and he says that after we had adjusted it he had nothing to complain of the selectiveness of the steering. My views are, from the run down here, that the selectiveness is as good as ever we shall get it. I have not found any wandering at all, and I have been running close on 90 M.P.H. There is certainly a big percentage of | ||