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).
Ignition timing for 20/25 HP high compression cars, detailing issues with detonation and comparing settings with low compression engines.
| Identifier | ExFiles\Box 5a\5\ 05-page119 | |
| Date | 5th May 1930 | |
| To HX. From Hs{Lord Ernest Hives - Chair}/AJL. c. to HY.{Tom Haldenby - Plant Engineer} X5771 Hs{Lord Ernest Hives - Chair}/AJL.1/W.S.5.30. X928 X1370 X5771 X5680 IGNITION TIMING ON HIGH COMPRESSION 20/25 HP. CARS. With reference to HX.7/T.S.5.30., we have asked the D.O. for the necessary ignition control alteration on all high compression cars. With regard to the last two paragraphs:- We are aware of the detonation which occurs when running on magneto ignition at low speeds fully advanced. Owing to the magneto ignition not having an automatic advance this is unavoidable. We already lose power at high engine speeds when using the timing of 5° P.T.D.C.; my later setting causes a large loss of power at high speeds. The old low compression engine timings as compared with the recommended high compression timings are as follows:- | | Low Comp. | High Comp. | |---|---|---| | Battery Ignition Full Retard Setting | 10° PTDC. | 10° PTDC. | | " Advance " (on quadrant) | 30° BTDC. | 13° BTDC. | | " " (quadrant and Automatic) | 60° BTDC. | 45° BTDC. | | Magneto " Retard Setting | TDC. | 5° PTDC. | | " Advance " | 36° BTDC. | 31° BTDC. | When it is realised that the high compression engine is naturally more prone to detonations and more sensitive to ignition control at high speeds, the recommended timings do | ||