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 engine performance comparing valve sizes, camshaft duration, and turbulence effects between various engines.
| Identifier | ExFiles\Box 102\5\ scan0132 | |
| Date | 24th June 1932 | |
| -2- Hs{Lord Ernest Hives - Chair}/Rn.{Mr Robinson}10/KL.24.6.32. As a matter of interest, we repeated a test trying small v large valves on the Phantom, and we got the same sort of results, Curve Rn.{Mr Robinson}24 attached. Quite a small difference in valve size had a measurable affect. We then found on Rn.{Mr Robinson}P22. that we could get back 50% of the top H.P. lost (which was not in any case very great) by increasing the valve lift and the low speed M.E.P. was not measurably altered. A further test shewed that with a short duration shaft, high lift was more effective than with a long duration shaft, which is to be expected, Rn.{Mr Robinson}P.25. Tabulating the valve area/litre of our various engines, we find that the R.{Sir Henry Royce} engine has only 1.346 sq.in/ litre against 2.59 for Peregrine; in view of the R.{Sir Henry Royce} engine performance it can hardly be said that a valve area per litre greater than 2.4 is necessary for good top power. If the small valve does give turbulence, as we think, there is a real advantage in two inlet valves/cylinder. We have plotted an 8 litre power curve that we got from Bentleys, against our own, Rn.{Mr Robinson}P.56. The valve area/litre, induction system, and compression ratio were the same for both engines. The main point of difference between the two engines is the camshaft and Bentley 2 valves/cyl. The point of particular interest is that they get such good high and low speed M.E.P. If we attribute the good low speed M.E.P. to turbulence, it is difficult to ascribe the High Speed M.E.P. to a better valve orifice co-efficient and yet we can offer no other explanation. The camshaft accounts for a certain amount at the top and yet with R.{Sir Henry Royce} engine cams we cannot reach their top M.E.P., Rn.{Mr Robinson}57. It is conceivable that the turbulent head has some effect on top power. We suggest that if Bentleys can run with 22° overlap, we can usefully try out more than the existing 5° on the 114° shaft, as it will certainly improve our power output. | ||