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).
Technical memo comparing the Phantom III and Phantom II engines, focusing on piston speed, stroke, and gearing.
| Identifier | ExFiles\Box 96\1\ scan0038 | |
| Date | 26th October 1935 | |
| [Handwritten Signature] GRY{Shadwell Grylls} x361 W/S. Sg.{Arthur F. Sidgreaves - MD} from E.{Mr Elliott - Chief Engineer} c. Wop. Hs.{Lord Ernest Hives - Chair} Hy.{Tom Haldenby - Plant Engineer} E.1/HP.26.10.35. re Phantom 3. - H.Hill. 88MS. Replying to your memo Sg.{Arthur F. Sidgreaves - MD}5/E.25.10.35, this gentleman has very largely answered his own letter when he implies that the requirements of the majority of our customers are very different from his own. In the first place I doubt whether he has actually tried Phantom 3. This alone I think would satisfy him on a number of points. To answer his queries in detail, first of all as regards axle ratio. The potential power of an engine is dependent on its total piston area and piston speed, or in other words the product of the force on the piston top multiplied by the distance through which it moves represents the work done. If the stroke is shorter it is necessary to run the engine at more revolutions per minute to realise the same piston speed. In the case of the Phantom 3 engine, the total piston area is approximately the same as that of the Phantom 2, but the stroke is 4½" instead of 5½", and hence to get the same piston speed the engine has to run approximately 20% faster, and the rear axle has to be geared 20% lower. There is no disadvantage in this as the piston speed is the true criterion of the magnitude of the disruptive forces which have to be withstood in the mechanism. All shorter stroke engines have to run faster and the actual revolutions per minute of the engine has very little significance unless corelated to piston speed, and the wear of the engine is certainly more related to piston speed than to engine revs. For anybody who wants to go fast we contend that it is the average speed that matters and not the maximum, and in this respect Phantom 3 should satisfy all demands. The high geared car which can get up to a phenomenal speed if given a long enough stretch of straight | ||