Report comparing the performance of various exhaust system arrangements for the Bentley III unit.
| Identifier | ExFiles\Box 99\1\ scan0160 | |
| Date | 9th May 1938 | |
| To By. {R.W. Bailey - Chief Engineer} from Rm {William Robotham - Chief Engineer} /Swdl. {Len H. Swindell} c. SG. {Arthur F. Sidgreaves - MD} c. HB. {C. E. Harcombe} c. HHC. c. Da. {Bernard Day - Chassis Design} c. Mx. {John H Maddocks - Chief Proving Officer} BENTLEY III EXHAUST SYSTEMS. Further to our previous tests of various exhaust system arrangements on the GHO. unit, figures have been taken on the B.III. The results are given on the attached curve S.39 and can be summarised as follows. With the standard B.III exhaust system on the B.III unit (Curve 5) the power developed is 108.5 BHP against 125.5 BHP open exhaust (Curve 1) at 3750 RPM or a 13.5% drop. By using a double outlet manifold (Ex.30724) with two complete Bentley systems (Curve 6) 119 BHP. is registered at 3750 RPM. or only a drop of 5% from the open exhaust figure. The twin Jaguar arrangement was tried on the double outlet manifold (Curve 4) and registered almost identical max. power as the two Bentley systems although falling off more rapidly at speeds above 4000 RPM. Curve (7) shows the production B.II unit and exhaust system developing 111 BHP. The present "mock up" system on 7.B.V. gives a very high power loss and some account can be given for the disappointing performance of this car at high speeds. The actual power at 3750 RPM. (Curve 8) is 102.5 BHP. or a drop of 18.5% from open exhaust. The power increase obtained with the double system follows proportionately the back pressure in the system and the simple effect of a freed outlet rather than any wave effect. We consider that the latter is affecting the middle speed MEP. where the MEP. loss is actually greater than at the high speeds and some investigation on this will be carried out. Regarding the actual manifold with the double outlets although only losing 2 BHP. at high speeds appears rather bottle necked and by tapering the main pipe into the outlets could undoubtedly be made so that there would be no power loss. | ||
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).