Power increase modifications for the 'China' 25HP engine, including timing, valve, and pipe specifications.
| Identifier | WestWitteringFiles\T\March1929-December1929\ Scan237 | |
| Date | 4th November 1929 | |
| HS. {Lord Ernest Hives - Chair} FROM R. {Sir Henry Royce} & E. {Mr Elliott - Chief Engineer} SECRET & URGENT. R1/M4.11.29. C/c to SG. {Arthur F. Sidgreaves - MD} WCR. BY. {R.W. Bailey - Chief Engineer} re. "CHINA(Experimental Engine)" ENGINE 25HP. POWER INCREASE. X5771 X1725 Referring to your report HS {Lord Ernest Hives - Chair} /ACL1/AD21129., we do not think there is much wrong with the timing if we follow Phantom 11. which we understand gives the following timing as well as the 116° between the cams mentioned on your chart. PHANTOM 11. MAXIMUM ACCELERATION. Diagram labels: IN.6°, 10 EX, 61 DIV., 57 DIV., IN.54°, 54 EX. This timing is at the moment the heavy acceleration start. Let us talk of nothing but maximum acceleration ever in future, and before taking timings set the tappet clearance to a standard of .015" instead of .013" or less. Regarding valve sizes the exhaust valve can be a little smaller - 1.3" - (because this valve is naturally heavier) especially as the engine will nearly always be running with the silencer. The exhaust should also have a thicker head, and will be in Austenitic steel, while the inlet will be in silchrome. The valve springs will be modernised - i.e. open ended, rapid rating and taper. Agreed that the induction pipe should be 1.5" bore throughout, and the passage between the cylinder bores 1.2", tapering to 1.5" at ends. Fortunately the venturi is the right way round in this latter. Agreed that the exhaust pipe down pipes should be 1.75" dia. I should like the gas passages in the cyl. head all to be 1.5 but we shall see what is possible with the existing cyl. studs and tappet rods. There will be alterations to the coreboxes for the head, and the pattern will probably require some modification to the exhaust and inlet pipe. Mr. Jenner is working under E's guidance to send you/a drawing quickly of modifications to head and pipes. A very hopeful improvement will be that to the bend where the gas passes the valve stem guide: it is still restricted in Mr. Lovesey's tests. (1) | ||
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).