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).
Report page comparing engine performance based on compression ratios, carburetters, valves, and ignition systems.
| Identifier | ExFiles\Box 19\7\ Scan102 | |
| Date | 1st April 1927 guessed | |
| contd :- -5- On Print No.4. is shewn the power output as obtained above with the two carburetters, large valves and the 5.45/1 comp: ratio compared with a standard Goshawk of 4.75 to 1 comp: ratio. These three factors i.e. compression ratio, low compression and larger valves, result in a maximum gain of 15.75 HP. or 28%. An engine with 4.45/1 compression ratio and fitted with the two Zenith carburetters has been tested on the road and its general performance and maximum speed was very considerably improved. We intend to test the large valves on the car when its performance would be expected to be still further increased. The only objection to raising the compression ratio is the increased tendency to detonate. Referring to the I.M.E.P. curves for the Lorraine engine, supplied with a previous report, we see that although a 5.9 to 1 compression ratio is employed the I.M.E.P. falls to the same value as the standard 20 HP. with its 4.75 to 1 ratio at a speed of 750 r.p.m. This may to a large extent account for its comparative freedom from detonation as from appearance there is no marked evidence that the shape of the Lorraine combustion space should be superior to our 20 HP. The fact that a small ignition advance is all that is necessary on the Lorraine appears mostly due to the use of synchronised ignition from opposite sides of the head because comparing the ignition curves with some figures taken on the 20 HP. we find the advance necessary on the latter is not very different to the Lorraine with single ignition. contd :- | ||