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).
Performance comparison and analysis for a proposed 2.8 Litre 4-cylinder engine against competitor vehicles.
| Identifier | ExFiles\Box 134\5\ scan0014 | |
| Date | 28th June 1939 | |
| 1133 BY c. Rm.{William Robotham - Chief Engineer} DA.{Bernard Day - Chassis Design}2/G.28.6.39. 2.8 LITRE 4-CYLINDER ROLLS-ROYCE. I have been considering particulars of the 4 cylinder 3¾ x 4½ car, by comparing some others which may be considered competitive with it. The information is from published tests, and is not more than 18 months old. It is of cars of the 2½ litre class, all of which are rather smaller than the proposed 4 cylinder, but they are all that I have got as yet round about that size. The 4 cylinder Willys is really too small to be in this class, but being of interest as a fair sized 4 cylinder, it is given separately. The information gives the time in seconds to accelerate from 10 to 30 m.p.h. on top gear, this being chosen because it is usually the best acceleration the car is capable of. From this the acceleration in ft. secs.² is obtained, assuming uniform acceleration, and then the performance the car should be capable of at 100 m.e.p. in the engine with two passengers is calculated from the weight, c.c. capacity, rear axle gear ratio and tyre size. The ratio of these two is the approximate M.E.P. at the road wheels, allowing for all losses. It is suggested that, in the table, the ratio g x 100 is of the nature of a figure of merit of the performance, meaning a good performance with a low M.E.P. The maximum speed is given as an indication of how much the low speed performance may have been sacrificed to the top speed. It will be seen that the best performance is given by the 4 cylinder Riley, which has also a good figure of merit in spite of a high M.E.P. This, however, is rather misleading as the top gear ratio of 5.5 is too low for a 4 cylinder engine, and is only possible because of the overdrive (3.97) but unfortunately no performance figures on the latter are available. The car is undoubtedly a good performer, however. If we try to imitate the two best cars, both of which are near our size, viz. the 16.9 Hudson and the 20 HP. Standard, and say we do not want a top gear ratio of lower than 4.5, we should require to weigh 28 cwts. The performance figures resulting are given in the table. This may be thought to be a weight too low to be achieved, but the Hudson and Standard weights are lower. If it is thought that we cannot attain this weight, due to using existing rationalised parts and standard bodies, then there is a value of η obtained on 3.B.50 with a C.I. 6 Cyl. engine, of 81.4 with single exhaust system. Assuming that we can repeat this on the 4 cylinder of | ||