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 engine performance using different spark plug positions, cylinder heads (No.2 Ramp vs standard Bentley), and exhaust timing durations.
| Identifier | ExFiles\Box 133\2\ scan0080 | |
| Date | 11th October 1934 guessed | |
| (4) when a small improvement is obtained. When two plugs in the side positions are used a very big improvement is gained. When one of the two plugs is fitted in the normal position, however, very little improvement over one plug only is obtained. The curves on Sheet 11 were obtained with the standard Bentley timing. The benefit to be obtained from the use of two plugs is also illustrated on Sheet 12; one pair of curves referring to the best timing at 3000 R.P.M. and the other pair referring to 4000 R.P.M. These curves are, however, only of academic interest as it would be extremely difficult to arrange for two plugs on a multi-cylinder Ramp head. POWER COMPARISON. A direct comparison between No.2 Ramp and the standard Bentley cylinder heads will be found on Sheet 4 of the curves. The full line curves represent the best all-round figures obtainable with No.2 Ramp head when the valve timing overlap is restricted to 12º. The "dotted-line" curves refer to the standard Bentley head. It will thus be seen that the No.2 Ramp shows an improvement of 8.0 lbs/sq.in. B.M.E.P. (7%) at 1000 R.P.M., 6.3 lbs/sq.in. (5%) at 2000 R.P.M., 8.0 lbs/Sq. in. (6.5%) at 3000 R.P.M. and 7.0 lbs/sq.in. (7%) at 4000 RPM. Of this improvement 0.5% is due to the slightly increased compression ratio. of the No.2 Ramp head. The valve timing used with the No.2 Ramp head closes the inlet valve fairly early (see paragraph under Valve Timing) and if this timing is used with the standard Bentley head (with its smaller inlet valve) a serious reduction of power takes place at speeds above 3500 R.P.M., but a useful increase is obtained below that speed. This is illustrated by the "long dash line" curve on Sheet 4. The remaining curves ("chain line") refer to the power obtained from No.2 Ramp when the timing overlap is not restricted. EXHAUST TIMING DURATION. The curves on Sheet 3 show the effect of an alteration in the duration of the period of exhaust valve opening, the inlet timing remaining normal. It will be seen from these curves that the normal exhaust timing gives the best results with No.2 Ramp head. (Contd) | ||