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).
Phantom II exhaust system and silencer design for the 20/25 and 40/50 models.
| Identifier | ExFiles\Box 14\6\ Scan255 | |
| Date | 29th July 1932 | |
| To E.{Mr Elliott - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} J7230. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}7/MJ.29.7.32. XS530 P.11 EXHAUST SYSTEM. You will have seen from the Brooklands tests that the Phantom wants a better silencer immediately. The silencer that we are standardising for the 20/25 has now completed 10,000 miles on 19-EX. and we believe with very slight modifications to reduce the noise when 'picking up' will be acceptable to Sales. We therefore propose to do the best we can with it, and try and get it on production, before we proceed with the larger dia. which we know to be necessary for maximum efficiency. Curve Rm.{William Robotham - Chief Engineer}P.59 shews an analysis of the losses in the 25 HP. resonance silencer fitted to a 40/50. It will be observed that at 3250 R.P.M. no less than 8 BHP. is lost in the entrance from the silencer to the fishtail (difference between curves 6 & 7) and a further 6 BHP. in the swan neck and fishtail itself (Curves 2 & 3). Now we know that this is completely wasted because restriction at this point does not reduce pick up noise appreciably; actually we were better on the 20/25 when we went to the P.11 size of fishtail. Therefore the first design we should like you to give us is a larger dia. exit from the silencer, fishtail and swan neck to fit on the existing 20/25 resonance type silencer. When we have this, we shall baffle the silencer internally until it is satisfactory. You will note that two baffles only drop about 4½ BHP. (Curves 3 & 7) and we therefore hope that the complete silencer may be 15-20 BHP. better off than the present standard. (The one running in France is 9 BHP. better than a P.11 short type). [Handwritten note on left margin: To be used on the 40/50] With regard to the completely new P.11 silencer. We know that we can with advantage use all the capacity we can get. If you will look into the matter and give us a sketch showing the outline of the largest chamber that you consider practical for the short type Continental P.11 we will make up the necessary experimental chambers of the correct dia. and evolve the best system of baffles etc. We should like a decision as to the cut-out. As you see this is now about 10 BHP. down on open exhaust at 90 MPH. Probably from the power point of view this is not worth bothering about, but there is also the control difficulty due to the expansion of the silencer to consider. If you do think it feasible to put it somewhere about the sliding joint let us | ||