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).
Graph showing engine performance with a modified cylinder head, pistons, and a 6.8:1 compression ratio.
| Identifier | ExFiles\Box 134\2\ scan0193 | |
| Date | 1st February 1939 | |
| -6- ② CYLINDER HEAD THROAT OPENED OUT TO PD 292 (SODIUM FILLED EX. VALVES) RAISED CROWN PISTONS. PD 304 WITH .100 MACHINED OFF TOP OF BUMPS. 6.8:1 COMP. RATIO MAX. POWER x---x NON DETONATING MEP lbs/D RPM IGN ADV °BTDC MEP IGN Curve (2). As Curve (5) but .100 machined off the top of the piston crown, which lowers the compression ratio to 6.8 : 1. This machining improves the non detonating characteristics compared with the full bump, but still falls short of curve (5). Continued. | ||