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).
Power output improvements from modifying engine valve and port sizes.
| Identifier | ExFiles\Box 133\2\ scan0115 | |
| Date | 1st November 1934 guessed | |
| - 3 - 1.25" diameter exhaust valve, also with 1.35" diameter inlet port. The valves were then progressively increased in size until the inlet was 1.5" diameter and the exhaust 1.4". The final modification consisted of enlarging the inlet port to 1.5" diameter and removing the inlet valve guide boss. POWER OUTPUT. A comparison of the "close-centres" head in its final condition with the standard Bentley head is shown on Sheet 1 of the curves. The power output of the former head is shown with normal Bentley timing and with the best timing for 3000 R.P.M., restricting the overlap to 12°. It will be seen from the curves that the latter timing gives the best all round improvement, although the high speed increase is not as great as with the former. On Sheets 2 and 3 will be found curves detailing the development of the "close-centres" head, each increase in valve size being shown. By comparing curve 2 (Sheet 2) with the standard Bentley curve (Sheet 1) the value of the better trepanning around the valves of the "close-centres" head will be seen. In its final condition (and with normal Bentley timing) the "close-centre" head gives very little increase over the standard Bentley below 2500 R.P.M., where an improvement of 3.0 lbs/sq.in. M.E.P. is noted. At 3000 R.P.M. this has grown to 7.0 lbs/sq.in., at 3500 R.P.M. to 9.0 lbs/sq.in., at 4000 R.P.M. to 10 lbs/sq.in. and at 4500 R.P.M. to 12.5 lbs/sq.in. In order to compare the two heads under "3000 R.P.M." timing conditions, the "dashed-line" curve on Sheet 1 must be examined in conjunction with curve 4 on Sheet 4. The superiority of the "close-centres" head will then be found to be as follows : - R.P.M. .... 1000 1500 2000 2500 3000 3500 4000 4500 MEP. Increase lbs/sq.inch 3.5 2.0 1.5 3.5 6.5 9.0 10.0 12.0 It is interesting to note that above 2000 RPM. these increases in MEP. are almost identical with either timing. | ||