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 for a standard engine using cast iron versus aluminium pistons, and a second test showing horsepower with varying numbers of rings on aluminium pistons.
| Identifier | ExFiles\Box 35\2\ scan 226 | |
| Date | 12th April 1920 | |
| 12.4.20. COMPARISON OF HP. TAKEN ON A STANDARD ENGINE FITTED WITH CAST IRON AND ALUMINIUM PISTONS. TABLE 1 H.P. R.P.M. | ALUMINIUM. Cut-out open. | ALUMINIUM. Closed. | CAST IRON. Cut-out open. | CAST IRON. Closed. 2250 | 86 | 75 | 84.5 | 73 2000 | 86.5 | 76.5 | 83.5 | 75 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. TABLE 2 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 | 13.3 200 | 7.3 | 6.8 | 6.7 | 6.3 | 5.6 | ||