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).
Design and testing considerations for a Spectre cylinder head.
| Identifier | ExFiles\Box 93\4\ scan0007 | |
| Date | 5th February 1935 | |
| SECRET PSN.1/MN.5/2/35. To BY.{R.W. Bailey - Chief Engineer} Copy to Mr. Hives. Mr/Ives. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} Mr/Parkinson. SMALL UNIVERSAL UNIT. SPECTRECodename for Phantom III CYLINDER HEAD. We send you herewith LeC 4338 of a SpectreCodename for Phantom III cylinder and large valve head for the above unit. It should be noted that a restriction has been placed in the inlet port to represent the limitation imposed by the push rods on the main engine. After initial testing this restriction should be removed and its effect evaluated. Two types of inlet valve are shown. The one with the double tulip represents the standard type of inlet valve on the SpectreCodename for Phantom III and should be tested first. It would appear that this shape of valve offers some restriction to flow near full lift, and the modified valve shape has been designed to overcome this. Comparative tests with the two inlet valves will show whether the stronger valve with the double tulip is causing any appreciable loss of power. The head as designed has a compression ratio of 6 : 1, but the roof can be machined off to give a compression ratio of 6.5 : 1. However, we are particularly interested in a compression ratio of 6.25 : 1 as this might prove a useful ratio for the main engine, so we should be pleased if the head could be machined to give this ratio before going on to the higher ratio of 6.5 : 1. The walls of the inlet port have been left rather thick so that the port can be machined out to a larger size at a later date if this is thought desirable. It should be noted that the cylinder block cannot be drained as it projects downwards into the top-half crankcase. This should be borne in mind and suitable steps taken if there is any likelihood of freezing. We should be pleased if you would send prints of the above LeC. to Hs{Lord Ernest Hives - Chair}/Wd.{Mr Wood/Mr Whitehead}, Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} and Hs{Lord Ernest Hives - Chair}/Parkinson in addition to the usual prints. E/ PSN. AMI LeC.4338 | ||