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).
Experiments on engine valve overlap timing.
| Identifier | ExFiles\Box 134\1\ scan0073 | |
| Date | 24th January 1938 guessed | |
| Experiments on Amount of Valve Overlap The general idea of opening the inlet early is to give a longer time of full opening. This is not so effective as might be supposed, but to understand the reasons would require a detailed exposition of cylr. filling, which I dont propose to give. I got cams made with 3 degrees of advance viz, 10°, 20°, 35°. The last one was incorrectly made for the other timings, but experiments showed that anything beyond 10° early was useful only with a very low exhst. press. sufficient to give some "blow through" from inlet to exhst. Such timing was very disadvantageous with even small back pressure in the exhaust. The conclusion is that while it is advisable to have the inlet opening quickly it does not require to be opened much before T.D.C. The Exhaust Valve, on the other hand, must not be closed at T.D.C. It is evident that this is so in theory because there must be a lag in the outgoing of the gas behind the piston motion, ie the piston must be exerting pressure on the gas & if the valve is nearly shut at T.D.C. | ||