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).
Technical memo discussing exhaust systems, including a comparison with Cadillac silencers and notes on noise measurement.
| Identifier | ExFiles\Box 173\1\ img281 | |
| Date | 12th February 1934 | |
| -3- He/Rm.{William Robotham - Chief Engineer}S/WA.{Mr Wallis}12.2.34. Cont'd.{John DeLooze - Company Secretary} They have accepted that you must use a noise measuring appartus for small differences. I shall go to the proving ground to see just what set-up they have. The enclosed paper gives some useful information for any one starting a series of tests. Exhaust Systems. You will have received the paper on exhaust systems that I sent you. It contains a number of novel suggestions, but I have met no one yet who is trying anything very different from what we are using ourselves. Nevertheless I feel that we should continue working on silencers as Cadillacs are doing better than we are with regard to weight and cost. One thing I think we should definitely try is a comparison of the 20/25 and Bentley heads on a 25 HP. car, also compare camshafts and compression ratio to get some idea as to how raising the efficiency of an engine affects silencing difficulties. Information obtain from Cadillacs is briefly. (1) They find the two 6 cyl. banks of the twelve far more difficult to silence than the two 8 cyl. banks of the sixteen. (2) They find the lowest silencer volume with which they can get satisfactory silence is four times that of the cylinder swept volume. (3) They use conical baffles in the silencer, a push fit on the outside diameter, and are not troubled with "clicking" or cooling. They get their worst clicking from the movement of the exhaust manifold. (4) They get silence with 2.5 lbs/sq.in. back pressure at 3000 R.P.M. of which 1.5 lbs is due to the skin friction in the down take and tail pipe apart from the silencer. | ||