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).
Analysis of the effect of reducing valve timing overlap on power for standard and 'close-centres' cylinder heads.
| Identifier | ExFiles\Box 133\2\ scan0116 | |
| Date | 1st November 1934 | |
| - 4 - VALVE TIMING OVERLAP. The effect of reducing the valve timing overlap is shown on sheets 4 and 5 for standard and "close-centres" heads respectively. From sheet 4 it will be seen that the overlap of the standard timing may be reduced to zero without a serious loss of power (2.5 lbs/sq.in.M.E.P. maximum loss) on the standard Bentley head. The loss is doubled, however, when the 3000 RPM. timing is used. The "close-centres" head (sheet 5) shows similar characteristics except that the loss at the higher speeds with standard timing is much greater than with the standard head. It will be seen from sheet 4 that the loss is very roughly proportionate to the reduction in overlap over the range investigated. The results are summarised in the table below giving comparisons of power at 1500, 2500 and 4500 R.P.M., the last two speeds representing the peak of the M.E.P. curve and a point just beyond the peak of the power curve respectively. | Head. | RPM. | Standard Overlap. | 0° Overlap. | | :--- | :--- | :--- | :--- | | | | Std. Timing. | 3000 Timing. | Std. Timing. | 3000 Timing. | | Stand-ard. | 1500 | 8.3 | 8.95 | 8.3 | 8.7 | | | 2500 | 14.6 | 15.20 | 14.4 | 14.9 | | | 4000 | 18.8 | 17.95 | 18.4 | 17.25 | | "Close-centres" | 1500 | 8.4 | 8.9 | 8.3 | 8.7 | | | 2500 | 15.0 | 15.7 | 14.8 | 15.2 | | | 4000 | 20.7 | 19.95 | 19.6 | 19.1 | The results on the "close centres" head with the 3000 r.p.m. timing (standard overlap) are equal to the results given by No.2 Ramp head under similar conditions (Report Hs{Lord Ernest Hives - Chair}/Wd.{Mr Wood/Mr Whitehead}CHP.1/GB.1.11.34). | ||