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 extract comparing the performance of C.I. (Cast Iron) pistons to other types.
| Identifier | ExFiles\Box 148\3\ scan0009 | |
| Date | 11th August 1920 | |
| S.H. 159 (100 T) (S.H. 159. 11-8-20) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 2800 X2748 Extract from OY1/G3.6.21. X.3764 (8) C.I.Pistons. X.3666 X.2748. These were bought from stock and are on the heavy side. The rings are the same as those used on service work at L.I. Service Station. The general design corresponds closely to the piston used at the Service Station during the war, but is somewhat heavier. It was necessary to obtain the closest thing to the service pistons which would take care of the shorter post-war connecting rod. If C.I. pistons should ever be standardised, we should recommend, from experience on service work with pre-war cars, something closely along these lines, but reduced in weight. A print of the standard service piston is enclosed. We will send later a sample of the actual piston. The clearances on the pistons on 4.EX is the same as used at the L.I. Service Station. The effect of fitting these pistons on 4.EX was to improve the slow running of the car very much indeed over the performance with the original aluminium pistons, which were themselves much better than the 4.ring pistons used on American production at that time (but since discontinued in favour of E-18688). With C.I. pistons it was found that the slow running performance was much less susceptible to fine adjustment of the carburetter. The slow speed hill climbing on top gear was better than anything we have obtained either with C.I. pistons on prewar cars or with aluminium pistons (4 or 6 ring) on post-war cars. The car will still run at 70 miles per hour. The tendency to chirp in accelerating is no more marked than with the original aluminium pistons, and though worse than on cars of American production, is probably due to the higher compression (25 cubic inches against 28 cubic inches on production cars). Spark plug trouble, met with frequently on production cars, is non-existent with the C.I. pistons on 4.EX. Against these advantages must be set the greater danger of seizure; possible greater wear of parts due to additional weight; possible tendency of preignition, etc. It should be emphasized, however that these troubles do not contd:- | ||