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 power output, weight, and reliability for different power unit configurations.
| Identifier | ExFiles\Box 148\5\ scan0115 | |
| Date | 1st September 1936 | |
| -2- (1) Power Output. With our 4 1/4 6-cylinder power units we have reached the limit of valve size and valve port which we can employ without lengthening the engine. The valve size dictates the power output. The only way we can get more power if we stick to the push rod operated, overhead valve, in-line engine, is to make the unit longer. A longer engine means more weight and cost and less room and comfort for the passengers. The primary advantage of the high power unit is that it enables the maximum amount of power to be obtained from any given length of engine. As far as single cylinder work is concerned, we say that for output the high power head begins where the present Bentley leaves off. If we take our T.T. head this year and reduce it to 6.5 - 1 C/R.{Sir Henry Royce} it gives 150 B.H.P. at 3750 R.P.M. Converting the high power single figures to a 6-cylinder engine as best we can, we expect 158 B.H.P. at 4000 revs. Assuming that we are optimistic, and that the power from the engines comes out equal, the valve sizes on the high power head at present are not up to their limit. (2) Weight. On the existing Bentley we cannot use an aluminium head because if we do we have no room for inserts, which are essential with this material unless we make the engine longer. There is plenty of room for inserts with the high power head. (3) Reliability. Our present stellited exhaust valves badly need inserted seats to prevent seat hammering. At the moment we have no room for these inserts. A high power head would give us plenty of room. | ||