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).
Cylinder head design, combustion chamber characteristics, and engine performance tests.
| Identifier | ExFiles\Box 134\2\ scan0096 | |
| Date | 11th November 1936 guessed | |
| -2- With regard to head shape and plug position they are sending us drawings of their latest cylinder heads. In general the throat shape is somewhat similar to that on our head but the combustion chamber is flat topped and straight sided with the plug near the centre. We propose modifying our existing head pattern to try this shape. It is interesting to note that the best m.e.p. curve they have obtained is considerably inferior to that we have obtained on our single cylinder head, and that they did not appear to have appreciated the potential improvements to be obtained with a larger inlet valve and short duration timing. The area of the throat between the cylinder and combustion chamber was considered to be critical and in their experience should be about equal to the inlet valve throat area. On our head we are a little less than this so that we might profitably run some tests with the throat opened out. They would not admit that this type of head was in any way inferior to their side valve cylinder heads as regards slow running, starting, slow speed pulling or detonation. However, the small amount of ignition advance required would seem to indicate a high rate of pressure rise and a potentially rough engine. We went out in a 16 H.P. Triumph fitted with a special engine with 8 : 1 C.R. The car could be started on top gear and once it was moving pulled away very evenly and comparatively smoothly with no detonation until about 20 m.p.h. was reached. Rather violent detonation came in between 20 m.p.h. and 30 m.p.h. but could be supressed by using the hand ignition control. We were given to understand that the engine had just been refitted into the chassis and that when the ignition was correctly set there was little detonation throughout the speed range. The engine was very rough at higher speeds but no detonation could be heard. The engine was run on Redline No.3 fuel and with 8 : 1 C.R. this represents a real achievement. They are sending us prints of the cylinder head of this engine. From the power curve of this engine which they have sent us it is noted that this engine maintains an m.e.p. of over 120 between 1000 and 4000 R.P.M. The maximum ignition advance required is only 15° which would indicate a rapid rate of pressure rise. | ||