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).
20 HP exhaust cut-out, comparing its performance and noise levels against the standard model.
| Identifier | WestWitteringFiles\L\Jan1924-March1924\ Scan88 | |
| Date | 1st February 1924 | |
| R.R. 403A (40 H) (SL 42 12-7-23). J.H., D.{John DeLooze - Company Secretary} ORIGINAL C EXPERIMENTAL REPORT. Expl. No. 4269 REF: Hs{Lord Ernest Hives - Chair}2/LG11.2.24. To R.{Sir Henry Royce} from Hs.{Lord Ernest Hives - Chair} c. to CJ. RG.{Mr Rowledge} c. to E.{Mr Elliott - Chief Engineer} DA.{Bernard Day - Chassis Design} c. to BY.{R.W. Bailey - Chief Engineer} WOR.{Arthur Wormald - General Works Manager} 20 HP. EXHAUST CUT-OUT. The exhaust cut-out for 5-G-11 is larger in diameter than the original one of this type fitted to 4-G-11. The inside diameter of the original 5-G-11 silencer was 1 3/8" - the one on 5-G-11 now is 1 5/8". We found that this larger pipe and larger diameter butterfly valves give us an improvement in power with the cut-out open and also increases the amount of noise. Attached is a chart which gives the losses with the cut-out open and shut. These tests were taken on 5-G-11 unit and with the silencer now fitted to that car. It will be seen that with the cut-out closed we get less loss in this silencer than we do with the present standard, at the same time, in our opinion, it is not sufficiently quiet with the cut-out closed. With the cut-out open we actually obtain more power than if we run with the exhaust pipe dis-connected from the exhaust mani-fold, i.e., the zero condition shown on the chart. We could not measure on the road any appreciable gain in speed with the cut-out open and closed. An average of a number of readings was less than 1 m.p.h., therefore the chief advantage of this cut-out is that it makes more noise. The reason we did not care for the single valve type cut-out and silencer was that this meant the exhaust always passing through the swan-neck pipe. 50% of the losses in the silencer occur in the swan-neck pipe so that contd:- | ||