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).
Comparison of horsepower (HP) for an engine with cast iron vs. aluminium pistons, and HP tests with different numbers of piston rings.
| Identifier | ExFiles\Box 77\3\ scan0232 | |
| Date | 12th April 1920 | |
| 12.4.20. COMPARISON OF HP. TAKEN ON A STANDARD ENGINE FITTED WITH CAST IRON AND ALUMINIUM PISTONS. H.P. ALUMINIUM. CAST IRON. R.P.M. Cut-out open. Closed. Cut-out open. Closed. 2250 86 75 84.5 73 2000 86.5 75.5 83.5 75 (6565) 1750 80 73 78.5 71.5 1500 72.5 67.5 71 67.5 1250 64.5 58.5 64.5 59.5 1000 52.5 48.5 51 48.5 750 --- 38.5 --- 38 600 --- 23 --- 23.5 400 --- 14.6 --- 15.0 200 --- 6.5 --- 6.6 Compression with both types of pistons 67 lbs. TEST SHOWING HP. WITH DIFFERENT NUMBERS OF RINGS FITTED TO STANDARD ALUMINIUM PISTONS. H.P. R.P.M. 6 rings. 5 rings. 4 rings. 3 rings. 2 rings. 600 25.0 24.5 23.5 22.3 21 400 16 15.6 15.0 14.5 13.3 (6666) 200 7.3 6.8 6.7 6.3 5.6 | ||