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).
Varying camshaft timing and its effect on cylinder pressure and inlet valve opening.
| Identifier | WestWitteringFiles\K\September1923\ Scan55 | |
| Date | 17th August 1923 guessed | |
| LIGHT SPRING CARD - G.11. FIRING. G.11. Camshaft timing varied. (a) Two teeth early. (b) Two teeth late. (c) Four teeth late. (crossed out) (d) Standard. The positive pressure bump in the cylinder is shewn on the card to be much the same for all conditions. The point at which the inlet valve opens, however, being varied, causes the actual pressure blown into the induction pipe to vary considerably as below. | Valve timing. | Inlet opens. | pressure in cylinder at moment of opening. | |---|---|---| | | | Taken off pressure time cards. | | 2 teeth early. | 10ºB.T.D.C. | 10.2 lbs. per sq.in. | | Standard. | 6ºA.T.D.C. | 5 " " " | | 2 teeth late. | 22ºA.T.D.C. | Atmospheric. | An observed phenomena is that the later the timing the earlier the depression commences in the cylinder. There are two possible explanations for this :- (a) The late opening of the inlet valve allows the suction created by the piston, more chance to build up. (b) The positive pressure in the cylinder prevents the piston from creating a suction - therefore, where the positive pressure is least i.e. late timing, the depression commences earliest. ------------------------ | ||