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).
Analysis of power loss and performance in various exhaust system configurations on a B.60 engine unit.
| Identifier | ExFiles\Box 124\1\ scan0057 | |
| Date | 29th March 1939 | |
| 104H r 623 To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} c. Da.{Bernard Day - Chassis Design} c. Da{Bernard Day - Chassis Design}/Ev.{Ivan Evernden - coachwork} c. Rm{William Robotham - Chief Engineer}/Wym.{G. Harold Whyman - Experimental Manager} Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}2/MH.{M. Huckerby}29.3.39. EXHAUST SYSTEM TESTS ON B.60 UNIT. An analysis of the Wraith type of exhaust system ECD.872/79/90 as adapted to a B.60 unit, has been taken on the test bed, the results of which are shown on the attached curve (S.82). Considering 4000 r.p.m. where maximum power is obtained under open exhaust conditions, the results can be summarised as follows. That 3 BHP is lost in a 2" tail pipe and 11 BHP in a 1 1/2 tail pipe, the total loss to the system with the former being 22 BHP-14" Hg back pressure and 30 BHP-20"Hg back pressure with the latter. The rear silencer loses 8 BHP and the front chamber 5 BHP, whilst the downtake pipe as "Y pieced" to the separate manifolds loses 3 BHP, also 3 BHP is lost to the actual separate manifolds. There seems little justification for using separate manifolds unless a duplex silencing system be used as the loss to the manifolds is approximately the same as experienced on various types of engines using a single outlet manifold. As the exhaust system is controlled by its quietness and freedom from booms on the road, we cannot estimate what improvement is possible in regard to the power loss and yet still maintaining the standard of quietness. An interesting test on this unit was the trial of duplex Bentley II exhaust systems which other than having no front expansion boxes were complete. These systems were separate throughout, each manifold being connected to a Bentley II system and the loss registered at 4000 r.p.m. was only 5 BHP with a back pressure of 4" Hg. Although the duplex system has inherent disadvantages both in respect of cost and weight, it is remarkably efficient from a power loss point of view. | ||