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 4 port and standard 6 port head on Phantom III.
| Identifier | ExFiles\Box 93\4\ scan0082 | |
| Date | 5th November 1936 | |
| To E.{Mr Elliott - Chief Engineer} c. to Hs.{Lord Ernest Hives - Chair} c. to Da.{Bernard Day - Chassis Design} c. to By.{R.W. Bailey - Chief Engineer} Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}15/JH.5.11.36. Comparison of 4 port and standard 6 port head on Phantom III. There is an appreciable gain in power by the 4 port head at high speeds, as shown on the attached curve SP.{Mr Spinney}38. The comparisons were taken with the standard type of 4 port induction system, Stromberg carburetter and water heated hot spot, the figures being those obtained under open exhaust conditions. The maximum increase is at 4000-4500 R.P.M. and is 25 B.H.P., the peak power being 207 B.H.P. at 3750-4000 R.P.M., whereas the standard 6 port head has a peak power of 189 B.H.P. at 3500-3750 R.P.M. Below 2000 R.P.M. there is little difference between the two heads with regard to the power output. At 500 R.P.M. the distribution is better with the 4 port head and maximum power is obtained at full throttle, whereas with the 6 port head, due to poor distribution and consequent loading up, it is necessary to throttle back several notches to get the best results. It will be noticed on the curve that the induction pipe depression is 5.00" Hg. at 4500 R.P.M. with the 4 port head and 3.600" Hg. with the standard head at the same speed, this being taken in the branch pipes which bolt up to the hot spot. These figures serve to show how much more efficient the breathing is on the 4 port head, now showing the carburetter and hot spot etc. to be offering considerable restriction. An induction depression of 5" Hg. is an extra-ordinary high figure, and if it is possible to bring this down to our normal Bentley and 25/30 HP. figure of approximately 2- 2.5 Ins. Hg. by removing the restriction in the carburetter, etc., we should appreciably increase the high speed power. | ||