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).
The purchase of American cars for comparison, discussing engine cylinder count and connecting rod stroke ratios.
| Identifier | ExFiles\Box 173\1\ img398 | |
| Date | 17th February 1934 | |
| To-Sg{Arthur F. Sidgreaves - MD}: from E.{Mr Elliott - Chief Engineer} C. Her: Hs.{Lord Ernest Hives - Chair} E.9/HP. 17.2.34. re Purchase of American Cars. Replying to your memo sg.{Arthur F. Sidgreaves - MD}14/E.16.2.34 I am in agreement with the recommendation to purchase a 16 cylinder Cadillac for the reason that this sets a standard of performance and smoothness considered by Rm.{William Robotham - Chief Engineer} to be higher than anything else he has tried, and it is the standard we want irrespective of the number of cylinders by which it is reached. I believe we can achieve the same result with a 12 cylinder engine and suitable mounting. With regard to the 6 cylinder Terraplane, I believe this also would be more useful than buying a straight 8 as we have already got a sufficiently good example of the latter. Nevertheless my opinion is that given equal chances the straight 8 will always produce a better result than the 6 as regards smoothness. With regard to connecting rod stroke ratio, the following table shows what we are using:- Engine. Length of conn: rod over length of stroke. 20/25 and) Bentley ) 1.77. P.2. 2.09. SpectreCodename for Phantom III. 2.08. J.3. 1.8. Straight 8. 1.92. You will see that we are definitely using longer rods on the Straight 8. We know these will be better for mechanical efficiency and for less internal deflection in the engine in balancing secondary forces as between the middle four cylinders and the end pairs. It is interesting to learn the Americans so strongly recommend that the connecting rod stroke ratio should be two, or greater than two. The 8 Cylinder Terraplane on the other hand is only 1.82. E.{Mr Elliott - Chief Engineer} | ||