Performance graph showing Mean Effective Pressure and Ignition Advance against RPM for a modified engine configuration.
| Identifier | ExFiles\Box 123\5\ scan0284 | |
| Date | 1st February 1939 | |
| -6- hm {Capt. W. Hallam - Head Repairs} /Swd1.2/MH. {M. Huckerby} 1.2.39. 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 MEP lbs/□ IGN RPM IGN ADV °BTDC 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 (3). Continued. | ||
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).