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).
Design consideration document for a four-port exhaust system, comparing it to Bentley and Wraith heads.
| Identifier | ExFiles\Box 134\1\ scan0038 | |
| Date | 8th November 1937 | |
| To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Ed.{J. L. Edwards} c. Da.{Bernard Day - Chassis Design} c. Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} c. Rm{William Robotham - Chief Engineer}/Wym.{G. Harold Whyman - Experimental Manager} 1129 FOUR PORT EXHAUST SYSTEM. Considerations of a four port exhaust system on a Bentley six port head (induction) and the Wraith head show the following design features:- (1) The centre port cannot be divided up on the six port Bentley head, as there is then no room for any sand between the inlet and exhaust ports making casting exceptionally difficult, and also causing excessive overheating of the charge. On the Wraith head this is overcome partly by the actual form of the head itself where the inlet and exhaust ports do not run so closely together, and partly by staggering the valves, taking each valve slightly nearer its respective side of the head, this, of course necessitating new rockers. (2) Port Shape. The two centre ports are brought between the existing push rod and steed positions without the necessity of moving them. These two ports are made of a rectangular section and the final area of each port is 1.350 sq.in. as compared with the area of the original port of 1.430 sq. in. The advantages of a four port exhaust system is that two exhaust manifolds and downtakes may be used, and in a case schemed out by the design office, whence most of the above particulars have come, two manifolds may be used in a slightly staggered arrangement. There is liable, however, in this case, to be a slight overheating of the dyanmo brush gear. On the O.H.C. engine, with a six port exhaust system, a gain of some 8% was experienced by merely splitting the manifold into two, and leading it into a standard front expansion box, and it is therefore considered that a similar gain might be experienced on a Bentley or Wraith unit if this continued | ||