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 power curves for a Phantom II engine using various carburetter configurations.
| Identifier | WestWitteringFiles\U\January1930-April1930\ Scan017 | |
| Date | 7th January 1930 guessed | |
| -2- by 3.25", the power was reduced a maximum of 3%. On an appended print we give three power curves taken on Phantom II engine with (a) Std. chassis carburetter. (b) R.R.C.H. carburetter. (c) Solex twin carburetter. Although we see that the maximum power given by the Solex is the same as with the Phantom there is a very appreci- able gain with the former at lower speeds. These power curves are with open exhaust. The Solex shows its maximum advantage at 1500 r.p.m. (39 m.p.h.) where the gain is 12 HP. or 13½%. It is at these lower speeds where we so much appreciate an increase in power; a very appreciable increase is necessary at maximum speed to appreciate any difference on the road because at this point the tractive resistance curve becomes very steep. Another curve shows the results with a single R.R. C.H. carburetter. The free choke area in this case was 1.190 sq.ins. The maximum power was higher than either the Solex or Phantom (8 HP. at 2600 r.p.m.) but it only held its advantage over a short speed range because below 2000 r.p.m. (55 m.p.h.) the curve fell rapidly below the Solex. These curves show up very well the characteristic of the twin carburetter - i.e. one choke to three cylinders - compared with a single choke carburetter. The power increase given by the Solex over our Std. carburetter at 1500 r.p.m. is equivalent to increasing the bore by .25" for the same M.E.P. This effect is of course with open exhaust and would be reduced somewhat with the silencer. | ||