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).
12-cylinder engine design, performance, and dimensional considerations including various bore sizes.
| Identifier | ExFiles\Box 4\1\ 01-page009 | |
| Date | 6th October 1932 | |
| (3) cylinder engine by virtue of its shorter stroke, smaller flywheel, and shorter crankcase enables the transmission line to be lowered together with the front floorboards and chassis frame. We believe the rear part of the chassis, with the help of the smaller road wheels can follow suit, and hence the whole car can be lower, which represents a direct gain in top performance. Referring now to engine size and output, we attach a blueprint showing the performances compared of various makes of 12 cylinder engines. Attention is drawn in particular to the lower part of the diagram showing the low value of the B.M.E.P. obtained, compared with what we are projecting. The induction system of the 12 cylinder car engine can be said to have more limitations than the six. Unless we can, and are prepared to fit four S.U. carburetters we can hardly expect to reproduce the J.1 performance figures on the SpectreCodename for Phantom III. We believe this emphasizes the necessity for pressing for improvements in the other directions indicated. As regards the question of engine size, it is possible within the present engine dimensions to cater for a range of bores as follows: Bore. Tax. Capacity. 3 £44. 6254 cc. 3.25 £52. 7338 cc. 3.4 £56. 8040 cc. As regards the stroke, the present design is for 4.5" and we do not recommend that this should be exceeded. There is no other twelve with a longer stroke than this, and all except the Lincoln are shorter. For aero work where the horse-power weight ratio is vital we came to the conclusion that the stroke should not exceed the bore by more than 10%. Any increase in the stroke demands still larger | ||