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 performance testing, focusing on camshaft timing, valve design, and carburettor comparisons.
| Identifier | ExFiles\Box 13\2\ 02-page093 | |
| Date | 12th June 1931 guessed | |
| - 2 - We have checked the effect of the short duration exhaust cam with a silencer and obtained approx. the same results as with open exhaust so that we think we are right. The nearest we have tried to the timing you suggest is an R.{Sir Henry Royce} shaft with 114° between the cams giving a timing at .020 (3) This dropped the M.E.P. all the way to 3000 r.p.m. as you will see by the attached curve sheet 3. and the amount gained above this speed is negligible. The 114° shaft is inferior to the 110° shaft over its whole range as you will also observe, we can therefore consider a 120° shaft as out of the question for a car to give any low speed performance. Valves. We attach a curve (sheet 5.) shewing the effect of the 1.95" valves (which we can get in without valve inserts) on power. [strikethrough] This shews that we have lost turbulence. [/strikethrough] We are doing some expts. improving the clearance round the standard inlet valve to see if we can pick up at top speed, also trying a set with 30° seats. The 4 litre Bentley curve suggests that they too loose low speed M.E.P. through the size of their inlet valve. Our results at present are inconclusive as to the inlet valve but say the exhaust valve could be smaller if we wanted to alter the inlet position. Carburetters. The Claudel we at present use has a depression of over 3" Hg. at top speed. The S.U. expert says they work with 7 - 9" of water over the whole speed range since they are practically a constant depression carb. This would give us a big advantage. There must be something in their claims as they are fitted to almost every fast car, i.e. Bentley, Invicta, M.G. (The small one now develops 40 B.H.P.) Their basic patents have expired. We are trying two Bentley carbs. on the P.II. Their air valve is beautifully made and appears to be a better scheme than ours. If we get the valves and [Text on first diagram] IO 12 18 EC 18 IC 56 EO 54 [Text on second diagram] IO 12 EC 14 IC 65 EO 60 | ||