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 L.HP figures and discussion of mechanical efficiency for 3.5 and 4.25 litre engines.
| Identifier | ExFiles\Box 133\1\ scan0204 | |
| Date | 13th May 1937 | |
| -5- Comparative L.H.P. figures are:- R.P.M. 500 1000 1500 2000 2500 3000 3500 4000 4250 4500 3½ litre. .106 .333 .724 1.30 2.125 3.180 4.460 6.06 6.92 7.90 4¼ litre. .164 .540 1.060 1.64 2.44 3.15 3.90 5.00 6.00 6.35 The variation in power loss between the two engines is not very great, which is only to be expected considering that there is very little difference between the 3½ and 4¼ litre crankcases, etc. Slight differences which do exist are probably due to variations in bearing friction between the two engines, and other individual characteristics. General conclusions. The motoring losses of an engine may be obtained in two ways, both of which give fairly similar results. The method of cutting out cylinders, however, takes a long time, and must be very accurately done if results are to be of any value. The method of direct motoring, however, is accurate and quick, but requires special tackle. The mechanical efficiency of the particular 4¼ litre unit tried was down at high speeds, on the 3½ litre job due to rather high pumping losses, and piston and big end losses. Reasons for these excessive losses are given above, and steps have been taken to lower the breathing loss by modifying the ports. When considering these figures, results over 3500 R.P.M. must be taken rather on trust as they are obtained by exterpolating from curves plotted from 500 R.P.M. up to 3500 R.P.M. The B.T.H. motor used on the job being incapable of higher speeds. They are, however, considered fairly accurate. Various other curves have been worked out for convenience of reference, figs Xll. and Xlll. giving the percentage distribution of losses. An improvement in the mechanical efficiency at high speeds would probably be rather difficult to obtain without some sacrifice of quality, and as the gain obtainable would probably not be in excess of 10 to 20 B.H.P. at an outside figure, it is not considered continued | ||