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).
Letter from Armstrong Whitworth discussing valve timing and characteristics for a 3-cylinder engine.
| Identifier | ExFiles\Box 133\3\ scan0075 | |
| Date | 25th May 1939 | |
| COPY. ARMSTRONG WHITWORTH SECURITIES COMPANY LTD., KADENACY DEPT., BUCKINGHAM AVENUE, TRADING ESTATE, SLOUGH, BUCKS. Our ref. HS.{Lord Ernest Hives - Chair}P.404. Your ref. Wd.{Mr Wood/Mr Whitehead}10/RS.{Sir Henry Royce's Secretary} 25th May, 1939. H.Wood, Esq., Messrs. Rolls-Royce Ltd., DERBY. Dear Wood, With further reference to your letter of the 20th inst., we have considered the timings and characteristics of the exhaust and inlet for the 3-cylinder engine, and we think that if you are to obtain the highest degree of efficiency a study should be made of the exhaust characteristics of 2, 3, and 4 valves. We should prefer 4 valves, purely from the Kadenacy point of view, but you may consider that to be too much of a complication. In order to get the best results at the high speed of 2500 r.p.m. we want the area of exhaust ports open before the air ports to be as much as possible, and yet the angle of exhaust lead to be as small as possible. In the case of a 4 valve engine the valves are, of course, very much lighter than is the case with a 2-valve and consequently they can be opened more rapidly. We, therefore, suggest that your designers make several lay-outs with 2, 3 and 4 valves, and see which gives the largest area at the moment of opening the air ports, and at the same time the smallest angle of lead. The following are the characteristics which we would recommend :- Area of Air ports 5.1/2 sq.ins. Period Air ports open. 96º Height of Air ports. .73 ins. approx. Exhaust Valve to open 78º before bottom dead centre Period of Exhaust Valve opening 105º [Handwritten note, bottom left]: 30º less than GM, a difficult problem, JNR{Charles L. Jenner}, [Handwritten note, bottom right]: Mr Jenner has a copy of this letter | ||