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 comparing engine performance based on port design, air flow, and valve size for Phantom and Bentley heads.
| Identifier | ExFiles\Box 31\2\ Scan106 | |
| Date | 24th August 1933 | |
| -8- As can be seen from curve 7, a variation is obtained between different ports of the same head - this can be due to differences in casting of these ports, or may be due to experimental error - as has already been mentioned. Hence, in comparing different port designs, it must be remembered that there may be an initial variation of flow to the above extent due to these reasons - before, one port can be said to be superior to another, it must give a very much better flow. On curves 6 & 10 are shown curves for Phantom & Bentley heads respectively with valves of different size - on curves 12 & 13 are shown their respective power curves. By a comparison of these the maximum power increase which one would expect from a head with a given air flow increase may be roughly estimated for the two types of head - e.g. comparing curves (4), (3) & (2) on curve 6 and curve 12, between (4) & (3) there is an air flow increase of 11.5% giving power increase of 4.5%, while between (3) & (2) air flow increase is 5.3% which should give power increase of 2% - actually power increase of 2.1% is obtained. It also appears that for consistent results, comparisons between heads must be made at about the same time and under similar conditions. SUMMARY. (1) The method of comparison used is excellent as a qualitative one, but in its present state not too reliable as a quantitative one. (2) The valve lift of the Phantom engine with the 2" diameter inlet valve can be usefully increased to give greater maximum power. Engine gear rattles at present are the limiting factor. (3) The valve size (inlet) of the standard Phantom head can be usefully increased to give increased maximum power - but the power increase so obtained is small. | ||