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).
Engine performance, focusing on cooler ignition plugs, compression ratios, and cylinder head modifications.
| Identifier | WestWitteringFiles\T\March1929-December1929\ Scan067 | |
| Date | 11th April 1929 guessed | |
| (2) necessary drilled out, inserting the drill through the water-ports provided for making connection with the cyl. block - see again fig.3 (3) USE OF COOLER PLUGS. An important point that should not be overlooked is that the RR. cyl. head as arranged for turbulence is reported to possess peculiar properties in protecting the ignition plugs from oil when the latter is present in excessive quantities in the cylinder. This, if true, appears to be a definite advance, and should enable us to use cooler running ignition plugs which will stand higher compression ratios without setting up pre-ignition, but at the same time will be hot enough for general running purposes. All engines can be said to be sensitive to sparking plug design, and it is not unusual to call for different plugs when the compression pressure is raised, to which there can be seen no objection if there is equal immunity from fouling of the insulators. (4) COMPARISON WITH PHANTOM. We had 5 to 1 compression ratio running on the big car engine for some time on 14-EX. very successfully, and there was no complaint of pre-ignition. Logically we can see no reason for not obtaining a similar result with 5.1 to 1 ratio on the 'twenty' given equal facilities for cooling the plug. (5) IGNITION ADVANCE. We should like to know what particular curve of ignition advance is being used with the turbulent head. Less advance may produce more satisfactory results with turbulence present. It is assumed that we are using the same degree of clearance between piston and cyl. head at top of stroke as on the big car engine. CONCLUSIONS. (1) It is suggested that there is a definite hot spot immediately under the plug on the actual cyl. head tested. (2) It is proposed to modify the combustion chamber to suit the lower compression ratio recommended as on LeC. 2689. (3) It is proposed to withdraw the plug slightly as on LeC.2689 (4) Consider cooler ignition plugs for use with this head. It may yet be found possible to use a higher compression ratio than 5.1 on the 'twenty', say 5.25, and with this in view a slight modification could be introduced into pattern instructions to leave the floor of the head about .050" thicker as shewn by the dotted line in fig. 2, LeC. 2689., so that the head could be produced to suit the higher ratio if and when required. E.{Mr Elliott - Chief Engineer} | ||