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 considerations for a 4.5 litre, 8-cylinder engine, comparing different configurations and materials.
| Identifier | ExFiles\Box 134\2\ scan0009 | |
| Date | 11th May 1935 | |
| -3- Hs{Lord Ernest Hives - Chair}/Smth.14/KW.11.5.35. Whether we use 2 inlet tappets or not, the inertia of the exhaust valve gear will mean that we must regard 5,500 as the max. permissible r.p.m. which would be given by an engine having a stroke of about 4.500". A 3⅛ x 4½ x 8 cyl. engine would have the following specification - Stroke/bore ratio 1.44 Capacity 275 cu.ins. = 4.5 litres Rated HP. 31.25 If we adopt an engine using an overhead camshaft a much smaller stroke would be an advantage since a higher r.p.m. could be used without valve gear trouble. A smaller stroke gives a lighter engine and slightly less power owing to the greater mechanical losses. A high power head engine will be heavier than one in which the combustion chambers are directly over the bores for the following reasons :- (1) The difficulty of making a satisfactory joint in the neighbourhood of the combustion chamber throat precludes the use of an aluminium block and liners. (2) The block and head will be about 3/4" wider than in the other type; (3) The exhaust passages are cast in the C.I. block, whereas in the other type they are cast in the head, which may be made of aluminium. To offset the above, the head will be about 1½" less high owing to the lowering of the position of the inlet valve. Incidentally this last factor will also reduce the differential expansion between the head and the valve gear, and thus may possibly enable us to dispense with hydraulic tappets. | ||