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 comparing valve openings, lift, and area for various engines.
| Identifier | ExFiles\Box 92\2\ scan0134 | |
| Date | 1st 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. C50 increased lift 1.35 .394 .292 2.22 25 HP. Standard. 1.35 .344 .255 2.22 40/50 New Camshaft Lec. 2918 1.9 .470 .246 2.106 40/50 Std. camshaft 1.9 .430 .226 2.106 | ||