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).
Modifications to the 20HP model, including increasing engine size and chassis length to create a 25HP version.
| Identifier | WestWitteringFiles\T\March1929-December1929\ Scan086 | |
| Date | 18th April 1929 | |
| HB.{C. E. Harcombe} FROM R.{Sir Henry Royce} (At Le CanadelHenry Royce's French residence.) SECRET. ORIGINAL R1/M18.4.29. REC'D AT WW. 22.4.29. 20HP. X5770 X5050 X5830 It is decided that we cannot keep the weight of our 20HP complete car down to that of the Chrysler and other 25HP. cars, so that we must increase the size and HP. of the engine as soon as convenient. Naturally this has always been before us, but whatever we do it will never satisfy everyone because the more it is increased the greater the total weight will become until we get into the same position. But everyone believes that a 20HP. equipment is not large enough for our second model, therefore it must be increased to 25HP - i.e. .25" on the bore, and it may later have .5" on the stroke. This latter suggestion would mean a new engine, new crankshaft and connecting rods, and looks as though our reputation would be hopelessly lost before it was in the hands of the customers. One feels it is much easier to ask for, than to get, and also I am not sure how the rest of the chassis would stand the increase - clutch, gearbox, back axle, seem none too large for the increase given below. It still therefore looks as though for the immediate production we must make the very best of our present engine and chassis for perhaps another 500 chassis, at least, by:- (1) Still doing all we can to keep down the body weights, and height, and width, but we must make them long enough for 6 seats when needed. We must continue to help coachbuilders for lighter body construction and accessories, (there is much hope in sight.) My idea of 3" on the chassis is to avoid the short and ugly scuttles by having only the D.{John DeLooze - Company Secretary} steering. It also keeps the roof down by the difference in the height of the seats. We must get this going quickly: it is now nearly two years old. (2) We have already increased the engine maximum HP. by 20% at say 10% higher revs., so we can have 10% lower gear than in the present large wheel standard. We should then get at moderate speeds - 30/50 MPH. - the 20% increase in torque all in acceleration or hill climbing. (3) Mr. Elliott has made the discovery and valuable suggestion that we can increase the cyl. bore from 3" to 3.25" with the present engine, which is about 17%. This would give us another very definite move, and be sufficient with (1) and (2) to meet our present needs. I have wired him to get it to Derby as soon as possible:(not a long or expensive job.) I am in hopes that: (1) We can at once let Sales have the 3" longer chassis when they want a 6 seater, and so save the weight etc of high bodies. (2) That we can at once give them the improved engine performance with the new head, exhaust, etc, - i.e. possibly for the 150. (3) That for the next 200 we can give them Mr. Elliott's latest suggestion of cyl. bore increased from 3" to 3.25". HP. rating I think goes up from 21.6 to 25.5HP. Whether we can increase the gear ratio more than the change given by the small wheels will be learnt later. I think the longer & heavier bodies should have 10% lower gear than the smaller & lighter ones. R.{Sir Henry Royce} | ||