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).
Engine valve overlap and timing considerations.
| Identifier | ExFiles\Box 134\1\ scan0071 | |
| Date | 24th January 1938 | |
| 12/60 1129 24.1.38. VALVE OVERLAP. From the various positions of the inlet open and exhaust close positions relative to TDC. and their effect upon the performance of the engine as mentioned on the attached note from Dr. Morrison, we assume that these are meant to apply to the main accelerations and deccelerations only. For example as representative of our engine there is a low constant velocity toe on our cams which extends to a lift of .013 at which lift it is subjected to the main accelerations and gives following timings over heavy accelerations. Inlet opens 6° Past TDC. Exhaust closes 6° before TDC. Actual running timing at correct valve clearance. Inlet opens 24° before TDC. Exhaust closes 24° past TDC. We know from experience that the overlap at these small valve lifts is sufficient to impair the slow running but have not done experiments at various timings with the toe cut out in respect of scavenging the cylinder of exhaust gas. As the quietness of the valves on seating is very important, we cannot shorten the toe, therefore these should be taken into consideration when considering the effect of the various valve open and close position. We give herewith the effect of altering the position of exhaust closing with the other opening and closing positions the same. (1) Valve timing over heavy accelerations, Inlet opens 6° past TDC. Inlet closes 45° past BDC. Exhaust opens 45° before BDC. Exhaust closes 10° past TDC. | ||