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 in a Bentley exhaust manifold and silencer system.
| Identifier | ExFiles\Box 86\3\ scan0221 | |
| Date | 13th April 1938 | |
| -6- Rm{William Robotham - Chief Engineer}/D.Lee.1/MH.{M. Huckerby}13.4.38. Manifold, the loss was 5.3 HP or 3.56%. So comparing these figures with the manifold and two silencers in parallel, which was 12 HP. loss or 8.06%, the loss with three of the six ports silenced is approximately half. Finally, an analysis was made of the standard production Bentley exhaust silencer in conjunction with the 6 port manifold (the manifold designed for the O.H.C. Bentley) nearly 5.6 BHP or 3.76% was lost in the manifold itself. The complete silencer was fitted to start with and the power lost through this was 21.1%. The tail pipe was then taken off and the power checked again, but there appeared to be no loss in this at all. Next the rear expansion box was removed - this box having a baffle plate in the centre, and a series of holes drilled in it,- the box was responsible for a loss of 8.7% of the total power. Then the 3ft. 6ins. of 2" dia. pipe between the middle and rear boxes was cut off - leaving now the front and middle boxes only - 3.22% was lost in this pipe. The middle expansion box was then removed together with 18" of 2" dia. pipe between this and the front expansion box. This was responsible for a further loss of 2.62%. Finally, a loss of 5.72% was due to the front expansion box and downtake pipe from the manifold. Summarizing, from results obtained, the slight difference in the 3 and 4 port manifolds does not seem to warrant altering the present design of head, whereas the power obtained by two downtakes into one silencer is an appreciable gain over our present system, two silencers in parallel appear to be the ideal scheme, unless our present exhaust silencer is modified. A point well worth development is the shape of the manifold and the effect of blending the ports in different ways. Rm{William Robotham - Chief Engineer}/D.C.R.Lee. | ||