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).
Cylinder head compression ratios for the 20/25 model using different gaskets.
| Identifier | ExFiles\Box 27a\1\ Scan175 | |
| Date | 5th December 1934 | |
| W/P - Sr. X4013 Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}17/KW.5.12.34. With regard to the cylinder head we have sent off for the 20/25, you can try two compression ratios with this. If you use a standard gasket you will get just over 6 to 1; if you use a metal gasket you will get 6 1/4 to 1. If you use a standard cylinder head with a metal gasket you will get about 5.85 to 1 instead of the standard 5.7. It may be that even this small increase in ratio will be of some use to you, in which case you can order some of these metal gaskets and fit them to any car you like, as we have done a lot of running on them. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||