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).
Effects of dual ignition, larger inlet valves, and indicated power on engine performance.
| Identifier | ExFiles\Box 133\2\ scan0081 | |
| Date | 11th October 1934 guessed | |
| (5). DUAL IGNITION. It will be seen from Sheet 5 that a very slight improvement is obtained by the use of two plugs. The curves also show the minimum ignition advance necessary for maximum power in each case. LARGE INLET VALVE. After obtaining all the necessary data with No. 2 Ramp in its original state, the inlet valve seat was re-machined to take a larger valve (1.600" dia.). This valve increases the area through inlet valve by 14%. The curves on sheet 6 show the power output of the unit, after fitting the 1.600" dia. inlet valve, with three different valve timings. Sheet 7 shows the effect of a gradual improvement in the orifice coefficient of the inlet valve, all the curves being taken with the best 3000 R.P.M. timing limited to 12° overlap. Curves (1) and (2) give a direct comparison between the 1.500" dia. and the 1.600" dia. inlet valves, from which it will be seen that the larger valve causes a reduction in power below 2700 R.P.M. but an increase above that speed. Curve (3) shows a definite increase throughout the speed range is obtained by cleaning out the inlet port. When the cylinder head is trepanned so as to give the same radial clearance to the larger valve as was obtained on the 1.500" dia, the power output is reduced at all speeds (Curve (4)). Sheet 8 gives the same comparisons when the best 3000 R.P.M. timing without limit to overlap is used. It will be onserved that the curves do not assume the same relative positions as the previous set. Here, the cleaning out of the inlet port does not help and the best results are obtained by the 1.600" dia. valve only (Curve (2)), with the exception of a small range between 2300 and 2950 R.P.M. when the smaller valve is the best. INDICATED POWER. On Sheet 9 will be found curves representing the indicated power and consumption of the unit when fitted with No. 2 Ramp and standard Bentley heads. These curves have been compiled by adding the motoring losses (sheet 2) to the power curves shown on Sheet 4. (Contd) | ||