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).
Testing and modifying a 'Japan' engine exhaust system to reduce power loss while maintaining silence.
| Identifier | ExFiles\Box 181\M13\M13.2\ img047 | |
| Date | 9th May 1931 | |
| To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} c. to Sg.{Arthur F. Sidgreaves - MD} Hor. c. to Da.{Bernard Day - Chassis Design} S. c. to Hy.{Tom Haldenby - Plant Engineer} HS{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}2/KT.9.5.31. X5230. JAPAN EXHAUST SYSTEM. We have been endeavouring to get a Japan engine ready for the road with an exhaust system that would be silent and yet not lose too much power. We have always been disappointed with the twin carburetter 25 HP. engine when run under road conditions. Graph (1) shows the power loss on the normal Japan unit fitted with the standard carburetter. It will be noted that the loss due to the exhaust system is only 3½ lbs/sq.in. MEP at 2000 RPM, whilst at 3500 RPM, 12½ HP is dissipated in the silencer. Graph (2) shows the result of fitting the Same exhaust system to the same engine fitted with twin carbs. It will be noted that the loss in the exhaust system has now risen to 13 lbs/sq.in. MEP at 2000 RPM, and 18½ HP at 3500 RPM. An analysis of where this loss occurs is shown on the same graph. Having justified our impression that the exhaust system was likely to cause an excessive loss in power, the next step was determine whether this loss was in the exhaust system itself or in the manifold. It will be remembered that we have previously demonstrated the very marked effect which the manifold can have on a 6 cyl. engine of high output when the back pressure is appreciable. We therefore fitted a P.II exhaust system complete to the Japan manifold, which is a castiron pipe of exactly similar pattern to the P.II. The results are shown in Graph (3). It will be noted from this graph that 75% of the lost power is regained by this alteration, but we are still disappointed with the amount of MEP. dissipated at the speed of maximum ramming, i.e. 2000 RPM, where the loss in the system is no less than 5 lbs/sq.in. We are therefore carrying out tests having a separate exhaust pipe from each port to the expansion box to see whether some means of alteration is necessary to the manifold when an MEP. of 120 lbs/sq.in. is exceeded. The following is a brief comparison of the dimensions of the major components of the two silencers. | ||