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 opening specifications across various engine types.
| Identifier | ExFiles\Box 13\2\ 02-page122 | |
| 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 CHINA | 1.35 | .394 | .292 | 2.22 25 HP. Standard. CHINA | 1.35 | .344 | .255 | 2.22 40/50 New Camshaft Loc. 2918 | 1.9 | .470 | .246 | 2.106 40/50 Std. camshaft | 1.9 | .430 | .226 | 2.106 PEREGRINE | 1.200 | .334 | .279 | 2.69 J1 | 1.40 | .400 | .285 | 2.37 6Litre BENTLEY | 1.38 | .335 | .242 | 2.00 | ||