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).
Petrol consumption and mechanical efficiency tests conducted under various road and shop conditions.
| Identifier | ExFiles\Box 183\M22\ img135 | |
| Date | 28th October 1920 | |
| Contd. -2- Hs{Lord Ernest Hives - Chair}1/LG28.10.20. that we were losing speed, we got less M.P.G. There is a fair range on the mixture where there is very little difference in the M.P.G. We found that with the magneto ignition firing 2" before the top of the stroke, ignition retarded, gave us the best results. We could fire earlier with no disadvantage but we could not obtain any better results. Test 1. The car was run at 30 M.P.H. - 1000 engine revs: The throttle open just sufficient to maintain the speed constant. The mixture and ignition were in the best position for economy. The petrol consumption was 10.4 pts. per hour. Test 2. The car was run in the Shop with the rear wheel jacked up and the top gear engaged. The engine was run at 1000 R.P.M. 30 M.P.H. The mixture and ignition were adjusted in the best position for economy. The petrol consumption was 8.3. pts. per hour. Test 3. The engine was under the same condition as Test 2. except that the top gear was disengaged, and the engine was running light. The petrol consumption was 7.8 pts. per hour. These tests show that when the car is running at 30 M.P.H. on a level tar-macadam road, approximately 80% of the petrol which is being consumed is being used to overcome the mechanical losses in the engine and transmission. This explains very clearly why it is we get such a big increase in miles per gallon if we stop the engine and let the car run free on all possible occasions. We have measured the mechanical efficiency of a 40/50 engine at 1000 revs; and find that it is 86%. this means that it takes 6 HP. to turn the engine at 1000 revs; per minute. On the road we find that if we test the car over the same piece of road at the same average speed, we get the Contd. | ||