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 roaring, investigating the relationship with valve timing, gas discharge and pressure.
| Identifier | WestWitteringFiles\K\September1923\ Scan53 | |
| Date | 20th September 1923 | |
| R.R. 493A (40 H) (SL 42 12-7-23). J.H. D.{John DeLooze - Company Secretary} -3- Expt. No. X.4229 REF: Hs{Lord Ernest Hives - Chair}3/LG20.9.23. EXPERIMENTAL REPORT. This conforms admirably with the theory e that with the valve timing advanced there will be the biggest discharge into the induction pipe and hence the greatest roar; with the timing retarded no discharge and no roar. To reproduce the conditions of roaring with the ignition switched off, the exhaust pipe was removed so that the back pressure due to the five cylinders which had to be firing on the bench to turn the engine over but which would not be firing on the road, would not produce misleading conditions. Cards were then taken with standard valve timing (see Fig. GV.) | Valve timing. | Inlet opens. | pressure in cyl. at moment of opening. | |---------------|------------------|----------------------------------------| | Standard. | 6° A.{Mr Adams} T. D.{John DeLooze - Company Secretary} C. | 6.75 lbs./sq. in. | This again satisfies the theory that the gas discharge causes the roar, for the positive pressure is very much the same as when firing and the roar is also much the same. In addition, the positive pressure bump increases above 2000 r.{Sir Henry Royce} p. m.{Mr Moon / Mr Moore} (see G.1V fig.) and falls off rapidly below 1750 r.p.m. so that one would expect the roar to disappear below 1750 but increase about 2000 r.p.m. It is just possible that the previous figures might have been a conincidence and the following experiments were tried as a check. We found that by increasing the exhaust valve tappet clearance we could produce a large positive pressure on the indicator card (Fig.G.lll.) If we therefore took a camshaft which would not roar with standard valve setting contd:- | ||