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).
Constant speed consumption tests for Bentley III carburetors using a Zenith Mileage Tester.
| Identifier | ExFiles\Box 147\5\ scan0157 | |
| Date | 29th October 1938 | |
| -3- Rm{William Robotham - Chief Engineer}/GR.{George Ratcliffe}3/JH.29.10.38. Constant Speed Consumption (Zenith Mileage Tester). Curves obtained with 7.B.V. are shown on the attached graph. In view of the inadequacy of the B.3.A. needles used on the Bentley III 1 1/4 carbs a new needle, RRX, had been obtained. This was designed to eliminate the 10 to 30 M.P.H. weakness and also assist the getaway on a cold start when the starter carburetter had cut out. This needle gave a satisfactory mixture for road running, but it will be seen from the curves that it is totally unsuitable from a consumption point of view. For some as yet undefined reasons the standard Bentley II LB1 needles cannot be used on the Bentley III 1 1/4 carb. since the jet tube of the latter is .010" smaller in diameter. Hence the complete jet tube assemblies were removed from the 1 1/4 carbs, standard B.II tube assemblies fitted, and figures obtained with LB1 needles. This was wholly satisfactory from a performance and consumption point of view. The figures were actually about 1/4 MPG down on figures obtained with the standard B.II 3.B.IV, but when multiplied up by the ratio of effective tyre circumferences to allow for 1" difference in tyre size, the figures practically coincided. CONCLUSIONS. From tests so far carried out it would appear that the standard Bentley II jet and needle assembly is vastly superior to anything yet obtained with the jet tube fitted as standard to the B.III 1 1/4 carburetters. With this assembly it is anticipated that while eliminating the flat spot so far associated with Bentley III, consumption would be almost identical with that obtained on Bentley II. Cont'd.{John DeLooze - Company Secretary} | ||