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).
Comparison of No. 2 Ramp and Standard cylinder heads, focusing on constructional details and detonation performance.
| Identifier | ExFiles\Box 133\2\ scan0079 | |
| Date | 11th October 1934 guessed | |
| (3) COMPARISON OF NO. 2 RAMP AND STANDARD HEADS (Contd). Constructional Details. No. 2. Ramp. Standard. Area past inlet valve (normal) .... 1.677 sq. ins. 1.450 sq. ins. " " " " (large) ..... 1.920 sq. ins. ---- Area past exhaust valve ............ 1.450 sq. ins. 1.160 sq. ins. Valve lift ....................... .400" .400" Inlet port diameter .............. 1.500" 1.350" Exhaust port diameter ............ 1.350" 1.350" Forced turbulence ratio .......... 1.79 1.82 The forced turbulence ratio of the original Ramp head was 1.56. DETONATION. A comparison of No. 2 Ramp head with the standard Bentley will be found on Sheet 10 of the appended curves. From these curves it will be seen that No. 2 Ramp head compares very favourably with the standard for freedom from detonation (in spite of its slightly higher compression ratio) when the valve timing overlap is restricted to 12°; this being considered the maximum permissible for good slow running. This restriction reduces slightly the power output, but also makes a very large reduction to the audible range of detonation: thus, at 1000 R.P.M. detonation is decreased from 67 feet to 37 feet, at 1600 R.P.M. from 50 ft. to 12 feet, and at 2200 R.P.M. from 32 feet to 1 ft. Comparing the figures obtained with 12° overlap timing to the standard Bentley, the No. 2 Ramp is 38% better at 1000 R.P.M., the improvement diminishing up to 1600 R.P.M. when the two heads are equal. Above this speed No. 2 Ramp is slightly worse; at 2000 R.P.M. the figure is 2.5 ft. against 1 ft. for the standard. No. 2 Ramp requires a speed of 2350 R.P.M. to be clear of detonation, against 2150 R.P.M. for the standard head. If No. 2 Ramp is tuned to give the maximum power, detonation does not cease until a speed of 3750 R.P.M. is reached. The effect of plug position on detonation is shown on Sheet 11, from which it will be seen that the side position, which is nearer the centre of the combustion chamber, is actually worse for detonation until a speed of 2050 R.P.M. is reached. (Contd) | ||