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).
Dynamometer performance comparison graph for various car makes with different exhaust setups.
| Identifier | Morton\M4.2\ img028 | |
| Date | 19th May 1921 guessed | |
| HUMBER. FREE EXHAUST. DODGE. FREE EXHAUST. HUP. - FREE EXHAUST. BUICK. - SILENCER FITTED. MARMON.- SILENCER FITTED. MIN: 1500 1750 R TAKEN ON DYNAMOMETER. | ||