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).
Engine economy, throttles, and choke sizes, with performance data.
| Identifier | ExFiles\Box 123\1\ scan0048 | |
| Date | 24th April 1940 | |
| - 3 - Tm/TAS.{T. Allan Swinden}4/JS.{Mr Johnson's Secretary}24.4.40. Curves A and B show the economy resulting in a change from 36 m/m to 30 m/m throttles. It is roughly: 13% at 20 M.P.H. 6½% at 30 M.P.H. and 5% at 40 to 60 M.P.H. Maximum speeds ran as follows: 30 m/m throttles, 1.1/32" chokes - max. speed 86 MPH. 36 " " 1.1/32" " - " " " 89¼ " 36 " " 1¼" " - " " " 90½ " The third result was obtained in order to show the effect of choke size. ½ MPH does not seem too high a price for the blessings bestowed, in spite of La{L. A. Archer} Salle increasing their 1940 choke from 1" to 1¼", and the relatively large choke size of the Buick. To return to the economy problem, an explanation is not easily forthcoming. One thing is certain, that if the jet sizes of the 36 m/m carburettor were to be reduced to give the consumption, curve B, flat spots would develop. This was not the case, hence it would appear that we have a clue to better economy on a car such as the Ripple on which we are prepared to limit top speed. This top speed should not now be limited by choke size as heretofore, but by throttle size. It had been suggested by Fisher of Strombergs that economy would result from throttle size reduction because at any given speed the smaller throttle butterfly would be wider open, and hence the "main jet" or economy portion of the carburettor range would be reached sooner. The suggestion was good, but the reasoning not too good. When the entry of the main jets was observed on a flat road in direct gear it occurred at exactly 14 MPH with both throttle sizes. Nor does it seem correct to argue that the economy is brought about by restriction of flow at the throttle, since this would have little effect at low speed, whereas in effect the greatest improvement is found at the bottom of the speed range. The following argument is, therefore, put forward: | ||