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).
Camshaft timing and performance tests for the 20-25HP (China) Unit.
| Identifier | ExFiles\Box 102\5\ scan0120 | |
| Date | 29th February 1932 | |
| For Files. X5090. 29. 2. 32. 20-25HP (China) Unit. (E.57177) 110.5º and 108º Camshafts. 110.5º Camshaft. In conjunction with 5.75:1 Comp Ratio, and standard carburetter. The most suitable timing takes place with the Inlet valve opening at (approx) 7º A.T.D.C. under these conditions, a max power output of 75.6 B.H.P. was obtained at 3000 R.P.M. The B.M.E.P. reaching a max of 102.3 lbs/sq.in. at 1000 R.P.M. under the above conditions, still retaining the standard carb: compared with the standard 251P. unit, having comp ratio of 5.4:1, and 110º Camshaft to E.54115. the gain is 23.5 B.H.P. at 3000 R.P.M. 108º Camshaft. The further comparison 108º Camshaft was tried. The only difference between the two camshafts being the angle between the cams. Three different timings were tried, the most effective having the inlet valve opening at (approx) T.D.C. It will be noticed also, on the appended curves, that the exhaust opening, and inlet closing, is slightly earlier in each case on this camshaft. By going one tooth earlier with the timing, it will be seen, that while there is a slight gain at low speeds, a fall off in power is noticable at high speeds. By going one tooth later with the timing; while gaining slightly in power at high speeds, the fall off in power is much greater in comparison at the low speeds. Comparing the curves of the two camshafts, it appears that the 108º is slightly the better camshaft. But the very small gain, would probably be unnoticable on the road. All tests carried out with 2" dia exhaust manifold, front expansion box, P.2 short type silencer with cut out open. | ||