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).
Virtues of an 8-cylinder engine compared to a 6-cylinder engine.
| Identifier | ExFiles\Box 69\4\ scan0098 | |
| Date | 2nd September 1926 | |
| TO-BJ. } FROM R.{Sir Henry Royce} WOR.{Arthur Wormald - General Works Manager} } HS.{Lord Ernest Hives - Chair} } DY.{F R Danby} } PRIVATE AND CONFIDENTIAL R3/M2.9.26. 6 AND 8 CYLINDER ENGINES. From time to time an 8 cyl. straight line engine for our large chassis has forced itself into my mind. Our original fear of the length of the crankshaft has prevented us going further into the matter, but there are certain reasons why this greater length may not cause any trouble in an engine properly arranged (Isotta was wrong). The addition of the 2 extra cyls. promises to get over many of the present engine troubles which we know of no other way of avoiding, and which limits us in getting the combination of the greatest smoothness with a good performance. As far as I can see the disadvantages of the 8 cyl. engine can with the present knowledge be avoided, and it would help enormously in enabling us to turn out not only a better engine, but an engine less dependent on the perfection of the mechanical details. The virtues of the 8 cyl. engine over the 6 are:- (1) That the variation in torque re-actions are reduced to nearly zero, and the compression ratio which is at present limited by the vibrations due to the torque re-actions can be increased, and this is the only way of getting good performance and economical consumption. (2) The overrunning vibration due to the weight of the pistons is reduced to about 1/20th of the 6 cyl., and the con. rod vibration to about 1/60th. (3) It has an advantage in the construction of a lower chassis owing to only a small flywheel being needed. (4) The half time gears should be a much easier problem to get right as the drive is smooth, and slack should not result in a backlash noise. (5) The starter problem is easier because we can turn the engine as slowly as we like without fear of it running on after a compression. (6) A powerful engine can be constructed with only 2 valves per cyl. without the use of large valves. (1) | ||