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).
Power output graph for a 4¼ Litre Bentley engine, comparing two different compression ratios.
| Identifier | ExFiles\Box 134\2\ scan0184 | |
| Date | 15th December 1938 guessed | |
| 4¼ LITRE BENTLEY POWER OUTPUT S. 58 ① B.II 6.6:1 C/R ② B.60 7:1 C/R WITH TEST BED EXHAUST SYSTEM SHELL PETROL BOTH HAVE SAME INDUCTION PIPES & CARBS B.H.P M.E.P NOTE:- BOTH CURVES ARE FOR NON-DETONATING POWER B.M.E.P (LBS: PER SQ INCH) BHP R.P.M | ||