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 and timing tests to address detonation and improve power output on a Bentley engine.
| Identifier | ExFiles\Box 134\2\ scan0142 | |
| Date | 23th August 1937 | |
| -5- Two types of valve were run, solid and stem-cooled, this latter being used to cure detonation troubles dealt with in section (2) above. Ultimately, on No.4 head, a solid valve was found O.K., and is recommended for use on a main engine. A further increase in valve size to 1.600" dia. was made, and though no direct comparisons have been made a slight gain appears to be evident. Considering results on the O.H.C. unit, however, the added weight of the valve and the increased gas pressure loading a 1.500" dia. valve is recommended, since even with this size bottom tappet wear is considerable. With the objective of low speed power in view, the exhaust duration was decreased to 215° with a timing of E.O. 35° BBDC; E.C. 7° ATDC, this giving about 3 or 4 m.e.p. more at 1000 R.P.M., and giving us the best low speed power. Previous to this alteration, the standard Bentley exhaust valve timing of E.O. 51° BBDC; E.C. 7° ATDC had been used, and had indeed been used throughout all the previous tests. The new timing was now adopted, giving a power output as shown in Fig. V.{VIENNA} when run with the test bed silencing system. It was now decided, however, to run curves showing power output against back pressure at constant speed, and a comparison of standard Bentley against the high power unit with the new timing gave results as shown in Fig. VI. This meant that at a high back pressure, instead of a gain in power at top speeds for the high power unit, there was a loss. Low speed m.e.p. did not appear to be seriously affected. Another test, however, showed that similar curves to standard Bentley could be obtained by increasing the exhaust duration to its old value, viz., E.O. 51° BBDC; E.C. 7° ATDC, this result being due, no doubt, to the greater time allowance for the gas to escape. The low speed power was, of course, reduced, but the response to back pressure was not adversely affected. Further work has to be done on this job, however. | ||