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).
Series of tests to eliminate induction pipe power roar.
| Identifier | ExFiles\Box 179\2\ img047 | |
| Date | 12th December 1931 | |
| ORIGINAL To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} c. to Sg.{Arthur F. Sidgreaves - MD} c. to P. c. to By.{R.W. Bailey - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}1/WJ. 12.12.31. x7070. x7080. INDUCTION PIPE POWER ROAR. We have now completed a series of tests on the elimination of this phenomenon. The history of the trouble is as follows :- 4/50. When we first fitted the Solex carburetter to the 4/50 we got pronounced ramming effect in the induction pipe at about 40 M.P.H. which improved the acceleration of the car to a remarkable extent. This carburetter was not fitted with any type of air intake silencer and therefore, though the roaring intake was noticeable, we considered that it would probably disappear when adequately silenced. Shortly afterwards we fitted a twin choke Zenith to the 25 HP. The power characteristics and induction pipe roar was almost identical with the Solex on the 4/50 and was not considered permissable for a luxury car. We made a somewhat elaborate air silencer for this carburetter and found that though we could remove all the ordinary suction noises the induction roar persisted unless we cut down the power to such an extent that the ramming was eliminated. At about the same time the R.M. twin choke came on test. The induction pipe roar was not so pronounced with this carburetter as with the Solex. We made some investigations which indicated that the Solex induction pipe diam. being smaller than the R.M. increased the ramming effect and hence the induction roar. We adapted the Solex pipe to the R.M. carb. which confirmed these conclusions (Rm.{William Robotham - Chief Engineer}-.36). CAMSHAFT. We decided that we might be able to get rid of the noise by a different camshaft. On the standard camshaft the roar was worst between 40 and 60 M.P.H. We tried the 114° shaft to L.S. 2918. The volume of the roar was altered very little but the period of greatest intensity was moved to 65 M.P.H. and above. INTAKE SILENCER. Numerous attempts were made to remove the roar by means of air intake silencers. These were uniformly unsuccessful. Our last attempt consisted of extending the normal type of concentric tube silencer to the valve cover through holes in the top of which air was drawn (Sketch & Photograph (1)). The resonance of this tube actually made the roar slightly worse than with the concentric tube silencer only. | ||