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).
Brooklands tests comparing different induction systems, including open exhaust, cut-out, and a long-type silencer.
| Identifier | ExFiles\Box 13\4\ 04-page011 | |
| Date | 23th July 1932 | |
| -2- BROOKLANDS TESTS. Prior to these tests we took a series of three tests on four types of induction system consisting of open exhaust C.O. open and complete silencer, shown in curves Rm.{William Robotham - Chief Engineer}P.53/54/58. These are useful in explaining the track results. Cut Out. It will be observed that the cut out open is something more than 1 1/2 BHP. down at 93 M.P.H. on open exhaust. If the cut out was at the sliding joint, we know by tests that we should pick up at least 7 BHP. We will report fully on this when we summarise the 40/50 exhaust system tests. Full Long Type Silencer. As everyone now realises, the losses in the silencer are tremendous. With the semi-expanding carburetter, the loss between the manifold and fishtail exit is 55 BHP. at 90 MPH. Furthermore, curve Rm.{William Robotham - Chief Engineer}P.54 shows that the silencer brings the peak of the power curve down to 2700 R.P.M. no matter what camshaft or carburetter is fitted. This means that with the C.O. closed we shall never do much more than 80 M.P.H. until we improve the silencer, our power at present is falling too rapidly at this speed. Since Hales have accepted the resonance type silencer on the 25 HP. in which the power loss is not much more than 5% at 3500 R.P.M. we are hopeful of being able to satisfy them on the longer car. Track Figures. Sheet (1) shows that the R.A. semi-expanding carburetter in its existing state is 3.5 M.P.H. faster than the standard carburetter and 2.65 M.P.H. slower than the two S.U's. with the C.O. open. This about confirms the power curve figures on Rm.{William Robotham - Chief Engineer}P.53. If we remove the air valve from the semi-expanding carburetter, which is at least equal to the proposed enlargement now being made, we can equal the S.U's. and lap at over 90 M.P.H. With the C.O. closed the figures are reduced about 5 M.P.H. all round. It will be noted that these figures were taken with 21" tyres. (Sheet (2) shows the result of fitting standard tyres which, coupled with the silencer tends to nullify the advantages | ||