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).
Test results on the Phantom II engine's power output in relation to choke size, depression, and camshaft performance.
| Identifier | ExFiles\Box 182\M19\ img248 | |
| Date | 2nd October 1931 | |
| ORIGINAL To E.{Mr Elliott - Chief Engineer} from Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}1/AD2.10.31. PHANTOM II POWER OUTPUT. ????? We have nearly completed the tests you asked for regarding the choke size required to give the 3" depression on the P.2 engine at 1500 R.P.M. and at the same time we are getting the choke size for a 2" depression at the same speed. Whilst doing this I have been looking out some of our previous curves to indicate how the power output of the P.2 engine varies with depression. Curve Rm.{William Robotham - Chief Engineer} P27 was taken with the original W.W. 120° camshaft. Whilst this is not the best camshaft for maximum power it is quite useful for showing the effect of various depressions on the power output. Curve 2. was taken with the size of S.U. which you have at W.W. fitted on a temporary pipe. This was a bad pipe for distribution and the hot spot was inadequate so that the distribution was not good and therefore the low speed power should not be taken very seriously. The high speed powers, however, are of interest. This size of S.U. is definitely too small for P.2. when used as a single carburetter, and as will be noted it gives 3¼" depression at 3250 R.P.M. The effect of increasing the depression from 2" to 3¼" at top R.P.M. reduces the H.P. by no less than 15 or about 10%. Curve 3. we have put in to show, what we already know, that if a twin carburetter is used it will give considerably less peak H.P. than the single at the same induction pipe depression. In this case the twin carburetter actually gave less depression than the S.U. but was 9 HP. down at 3250 R.P.M. A similar curve on the 25 HP. shows that when going from 2.6" depression at 3250 R.P.M. to 3.9" depression, the top output is reduced by 7 HP. or again nearly 10%. Naturally, the better the camshaft the more benefit we should expect to derive from the lower depression and in neither of the curves attached can the camshaft be said to be ideal. It will be seen that our tests do not confirm exactly that the B.H.P. is proportional to the absolute depression in the induction pipe, but the output appears to vary more than one would expect from this law even with only moderately good camshafts. | ||