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).
Test report on carburettor and induction pipe configurations, including a blueprint for a single S.U. induction pipe.
| Identifier | ExFiles\Box 179\2\ img050 | |
| Date | 12th December 1931 | |
| -4- A further test with this balance piece was then carried out joining the two halves of the induction pipe by means of a pipe 1.25" dia. This resulted in a further 60% reduction in the roar which in this condition was almost passable. (Sketch 4). The metering and 'snap opening up' were of course completely upset, also the slow running. With the balance in the induction pipe only, 25% of the roar returned. A final test was carried out with a single 2½" throttle dia. S.U. arranged on a pipe as sketch (5). This scheme was not so good as the two balanced S.U's. and much the same as the balanced R.A. twin carb. for roar but of a different type, as there was little critical speed in the roar but a consistent amount of induction pipe noise from 50 M.P.H. upwards that one would not like to tolerate if there was any alternative. Sketch (5). [Blueprint Diagram of SINGLE 2.5" S.U. INDUCTION PIPE] ROAD PERFORMANCE OF CARBURETTERS POSSIBLE FROM POINT OF VIEW OF INDUCTION PIPE ROAR. Curve Rm.{William Robotham - Chief Engineer}P.46 shews the power and M.E.P. of all the induction systems we have so far tested on the 4 1/4/50 that might be considered passable from the point of view of induction pipe roar. They consist of :- (1) Standard Carburetter. (2) Balanced twin Common pipe and balance above chokes. (3) Separate balanced S.U's. (2). (4) Single Large S.U. We think that considered only from the power curve point of view, Nos. 2 and 3 are the best type for road conditions, as they give maximum M.E.P. just where it is wanted i.e. between 25 and 50 M.P.H. The only query is what kind of choke can we use in the twin carb. and get away with snap acceleration, this we shall know as soon as we have corrected the diffusers. If we have to cut down the choke sizes much we shall of course lose top power. No.4, the Single Large S.U. is excellent for top power. | ||