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 development and testing of a modified cylinder head, detailing iterative changes to its compression ratio and performance characteristics.
| Identifier | ExFiles\Box 134\1\ scan0167 | |
| Date | 12th October 1939 | |
| -3- Rm{William Robotham - Chief Engineer}/swdl.{Len H. Swindell}2/JH.12.10.39. This is confirmed by the condition of the cylinder head gasket when carrying out detonation loops, i.e. M.E.P. against advance. As far as can be noted on the bed the idling with the sloping valve head is slightly better than the E.R.S. head and this slightly better than standard. Although this report refers to the standard head it must be noted that this head has been machined on the face to bring its compression ratio in line with the others. The development of the EX.1383 head was as follows - (a) In original state at 6.4 : 1 very badly down for power. (b) In modifying the throat to make the alteration to the cross sectional area more gradual EX.1384 very little difference noted from (a) i.e. poor power but good for detonations. (c) Machined away the turbulent lip to EX.1758 thus reducing the compression ratio to 6.1 : 1. In this condition the power came up to standard, for the compression ratio yet retained the good anti detonating characteristic. (d) .050 machined off the face bringing the compression ratio up to 6.45 : 1 gave corresponding power increase for the ratio increases throughout the range and detonation at point of max. power. (e) Further .050 machined off the face which necessitated losing 1 - 2 lbs.sq.in. M.E.P. to cut out detonations on (Redline) now at 6.9 : 1 ratio. (f) The final modification was to recess and let the sparking plugs to the combustion chamber face (EXS.1869). The effect of this was some improvement in idling and less sensitive to ignition advance alteration. The cylinder head in its condition (d) was tried on the road on 3.B.30. by Rm{William Robotham - Chief Engineer}/Sym. who confirmed our tests in that the head was good for freedom from detonations with some improvement in idling. Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} | ||