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 modifications concerning exhaust bends, supercharging arrangements, and carburetor comparisons.
| Identifier | ExFiles\Box 140\1\ scan0158 | |
| Date | 12th April 1935 | |
| -2- Our next move was to replace the round bend in this arrangement by a square one, with the idea of breaking up the petrol stream and improving distribution. No improvement was noted, however. The slow running was no better when the induction pipe was exhaust heated with all the exhaust gas passing through the jacket. Referring to the appended sketch, the superiority of the first arrangement as regards slow running appears to be due to the greater length of the intermediate pipe and also to the fact that in the first position the angle with which the pipe enters the manifold effects the centrifuging effect of the blower whereas in the other it aggravates it. It has now become fairly evident that whatever scheme we adopt for the supercharging of the Bentley, the blower will have to be above the manifold, otherwise, if we are to use a spiral bevel drive, extensive alterations to the engine will be necessary. Furthermore, it will be difficult to avoid loading up with any other arrangement embodying a downdraught carburetter. We know that good results can be obtained with a fairly long intermediate pipe sloping down all the way from the blower. We are about to try a scheme of this type involving a short intermediate pipe. Carburetter. All our recent running has been done on either a Stromberg 42 mm. or a Zenith 48 mm. downdraught carburetter. As regards power and acceleration, each of these appears to be equally promising, but the Stromberg appears to be the better slow runner. The Zenith has the advantage of being 2" shorter than the other since it incorporates a starter carburetter in place of a strangler. Up to the present we have not been able to get decent acceleration with a choke size greater than 37 mm. on the Zenith, although the acceleration pump capacity is large. We think that at a later date it may be well worth while to try an arrangement with the accelerator pump injecting into the intermediate induction pipe, so that the capacity of the blower will not adversely affect acceleration. If this succeeds, we shall be able to use a much larger carburetter. | ||