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).
Outlining conclusions on camshaft design, its limitations and performance characteristics across various engines.
| Identifier | ExFiles\Box 13\2\ 02-page086 | |
| Date | 5th June 1931 | |
| To E.{Mr Elliott - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} 8799 Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}1/KT. 5.6.31. x5090 CAMSHAFT. With further reference to our conversation this afternoon, the conclusions we have formed on camshafts so far are as follows. We are limited on the duration by the slow running, low speed power, and possibly induction pipe roar. We are limited on the valve size by the disposition of our combustion chamber and the fact that on the 40/50 we have aluminum head with inserts. It would therefore appear that we ought, if possible, to open our valves with the maximum speed and lift them as far as possible in order to overcome our unavoidable limitations in other respects. On the F.{Mr Friese} engine cam, the heavy acceleration is equal to .00535" per division. On the Phantom II it is only .0038" per division whilst on the 25 HP. it is only .0035" per division. We do not know what the formulas past the lifting valve mean in actual breathing gain to the engine, but they indicate that the 30º seat is better than the 45º seat. This would seem to be a feature where we might gain a little power without any other disadvantage. With regard to the masked inlet valve, naturally we have had no experience of this, but where a short duration inlet valve is a necessity for a low speed power it would appear to have the fundamental advantage in that it enables the inlet valve to start opening at a much greater velocity than can be possible with the ordinary toe. The velocity of our car inlet valve is greatest when the valve has lifted .27", but at the end of the existing toe its velocity is only about 5% of the maximum. We cannot help feeling that some of the troubles we have had with exhaust valves on the 25 HP. are due to the length of the toe that we use, as these little valves seem to start to show signs of overheating at MEP's which are altogether lower than our standard practice on the aero engines. We shall endeavour to let you have all the information we can get out of the aero camshafts, but naturally we had never any idea that they would be suitable for the road as they stand, and they were evolved entirely as a means of getting information for future design work. | ||