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).
The effects of pre-ignition on Dadia IV and cast iron engines, comparing turbulent and cast iron cylinder heads.
| Identifier | ExFiles\Box 19\7\ Scan135 | |
| Date | 18th April 1929 guessed | |
| contd :- -2- temperatures very near that of the bronze inserted plug seats. Effect of pre-ignition on Dadia 1V. and cast iron engine. When the turbulent head engine with 5.6 : 1 comp: ratio is opened up to full throttle at 2500 r.p.m., pre-ignition takes place (when using the standard K.L.G. Kl plugs) immediately the engine has settled on its load which becomes manifest by rough and irregular running with a drop of about 10 to 15 HP. The water temperature has no noticeable influence - preignition occurring as readily with water at 35°C as at 80°C. Usually two or three cylinders only suffer from pre-ignition and on this particular head they were Nos. 1. 2. and 3. If these plugs were shorted out the engine would continue to run without further loss of power. We found that pre-ignition occurred with the cast iron head using 5.4 : 1 comp: ratio and similar sparking plugs, but did not develop so readily as with the turbulent head. The interesting fact was that the symptoms were entirely different as there was no loss of power even with several plugs pre-igniting. Apart from slight roughness, which however was less than with the turbulent head, the only direct evidence of preignition was by shorting out the offending plugs when the engine would, as before, continue to run without loss of power. We think the difference in behaviour between the two engines under the influence of preigniting sparking plugs, may be explained thus ; The turbulent head engine requires an ignition advance of 35° before top centre at a speed of contd :- | ||