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).
Technical memorandum comparing engine performance based on valve size, lift, and duration of opening for 3' Bore 'China' and 3.25' Bore 'J.1' engines.
| Identifier | ExFiles\Box 102\5\ scan0131 | |
| Date | 24th June 1932 | |
| XS990 To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Rn.{Mr Robinson} c. to Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} c. to Da.{Bernard Day - Chassis Design} E.{Mr Elliott - Chief Engineer} c. to By.{R.W. Bailey - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Rn.{Mr Robinson}10/KT. 24.6.32. XS770 VALVE SIZE, LIFT, & DURATION OF OPENING. With reference to HL/M.11.5.32. We have, during the past three years, collected a certain amount of information re the effect of power output, of valve lift and dia, which it would perhaps be useful to summarise. You mention our original 3" bore China engine out of which ACL. obtained good B.H.P. with .344 valve lift. The outputs of this unit at the time was exceedingly good, being 29.3 B.H.P. per litre. It was, however a test bed result as the carb. depression was too low to give reasonable low speed results. We have had 29.6 B.H.P/litre out of J.1. suitable for running on the road, which at the equivalent depression to the 3" bore engine is a better power output. The major differences between the method of obtaining power on the two engines was that originally large valves with a small lift were employed, and latterly smaller valves with a higher lift were used. Comparison of J.1 and 3" Bore China Engines. 3" Bore China. 3.25" Bore J.1. Inlet Valve Throat dia. 1.4 1.4 Inlet Valve Area/Litre 2.82 2.57 Duration Inlet Valve (.020 clnce) 224º 228º Max. B.H.P. attained. 92 108 B.H.P./Litre. 29.3 29.6 Induction Depn. 2750 r.p.m. .7" Hg. 1.3" Hg. Compression Ratio. 5.45 5.45 Small v Large Valves. When we put the larger inlet valves in the 3" bore China, we noticed a drop in the low speed, M.E.P. We attributed this to loss of turbulence | ||