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 development, valve timing, and plans for a Straight Eight and a 5-litre Six-cylinder engine.
| Identifier | ExFiles\Box 148\2\ scan0021 | |
| Date | 26th October 1938 | |
| -2- Power. Whilst we believe that we have not yet got the correct valve timing to obtain the best out of this engine, it has been demonstrated that it is possible to run with about 8% more M.E.P. at the intermediate speeds for the same amount of detonation. This confirms the promise shown on the single cylinder unit. Until the unit has been fitted into a car it is impossible to say whether full advantage can be taken of this increase in torque without roughness being transmitted to the occupants of the vehicle. We are, therefore, putting a second engine in a car as soon as possible. In order that development may proceed with reasonable speed both on the road and on the test bed, it is necessary to have at least six engines, and it is proposed to go ahead with these, incorporating in them any modifications as and when these are found to be necessary. We consider that we are now justified in going ahead with the development of this engine fairly vigorously, because although, of course, we have had various troubles, we have as yet had no indication that we shall be unable to give at least as good a performance on the road as the existing engine, and the advantages of cost and weight have been established beyond dispute. Experimental Variations of the High Power Head Project. Straight Eight. We hope that it will be possible to have a Straight Eight engine running before Christmas. 5-litre Six-cylinder engine. In view of the general desire on the part of Sales for improved Bentley performance, designs are being completed for increasing the capacity of the 6-cylinder cast iron engine to 5 litres. This is the biggest engine that can possibly be got out of the overall dimensions that have been established and, though we consider this well worth going ahead with experimentally, would like to emphasise the fact that even if it gives promise it will not be available for production for a very long time. We do not want to repeat the trouble which we ran into on the 4¼-litre Bentley when we increased the bore without putting up bearing sizes. There are indications, however, that the overdrive may have so entirely altered the bearing position that larger engine displacements will be possible with the same crankshaft. | ||