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 policy, comparing overhead, side valve, and push rod engines with reference to American designs.
| Identifier | ExFiles\Box 134\2\ scan0112 | |
| Date | 31th May 1937 | |
| -2- inlet side valve exhaust, which we believe can fairly easily be made. At the present moment, the overhead inlet side valve exhaust is still showing considerable promise, and it does, in addition, offer some manufacturing advantages. On graph 3 we have drawn a curve showing how this would compare with the best the Americans have done if it lived up to our expectations. You will see the M.E.P. of the 1938 Buick quoted in the curve No.1, and that this represents a big advance on the 1937 figures. It is the sort of improvement we are looking for. We understand it has been obtained by controlling combustion with an unsymmetrical piston crown. If we forget about this curve, and compare 1937 push rod and side valve figures only (curves 2, 5, 7 and 8), no one could justify the additional weight, complication and expense of the O.H.V. engines on the basis of better power output. In actual fact the Terraplane beats them all. Hence for economical transport it is clear that the Americans are right in using side valve engines. How, therefore, can we justify our present engine policy ? The answer would appear to be as follows:- (1) A certain section of the British public is still sufficiently mechanically minded to be under the impression that overhead valves represent improved efficiency. This type of construction, therefore, has some pyschological value. (2) Buicks have obtained a 10% improvement in efficiency, which they could not disclose, but which will be incorporated in their 1938 cars. This should be directly applicable to push rod engines only. We consider it to be imperative that we should obtain one of these Buick cars as soon as they become available, which will be about November of this year, so that we can find out what they have done. (3) It is reasonable to suppose that a push rod engine is better suited to supercharging than a side valve unit. | ||