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 table of car weights and required engine sizes to achieve a consistent power-to-weight ratio.
| Identifier | ExFiles\Box 126\3\ scan0002 | |
| Date | 6th October 1932 guessed | |
| CAR. | Wt. OF CAR EMPTY. | REQUIRED ENGINE SIZE TO GIVE SAME WT RATIO. POWER | LITRES OF ENGINE/TON OF LOAD. New Ford. | 25 cwts. | 3620 cc. | 2.9 25HP R.R. | 35 cwts. | 5060 cc. | 2.9 P.II | 50 cwts. | 7250 cc. | 2.9 | ||