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).
Tabulated list of valve opening specifications for various engine types.
| Identifier | ExFiles\Box 182\M19\ img215 | |
| Date | 5th August 1931 guessed | |
| TABULATED LIST OF VALVE OPENINGS. Engine | Dia. of inlet valve | Lift of inlet valve | Ratio lift/valve dia. | Valve area per litre disp. F.{Mr Friese} engine | 1.625 | .550 | .337 | 2.20 R.{Sir Henry Royce} engine | 1.950 | .570 | .292 | 1.84 25 HP. .050 increased lift | 1.35 | .394 | .292 | 2.22 25 HP. Standard. | 1.35 | .344 | .255 | 2.22 40/50 New Camshaft L.e.C. 2918 | 1.9 | .470 | .246 | 2.106 40/50 Std. camshaft | 1.9 | .430 | .226 | 2.106 | ||