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).
Power loss in the 25 HP exhaust system and recommending modifications to improve performance.
| Identifier | ExFiles\Box 5a\5\ 05-page132 | |
| Date | 6th May 1931 | |
| To By.{R.W. Bailey - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} X5771 Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}9/RT.6.5.31. 25 HP. EXHAUST SYSTEM. X.5230. X.5771. Now we are getting more power out of the 25 HP we find that we are losing far too much power in the silencer system. The original 20 HP. developed 55 HP. at 2750 RPM. our latest engine is developing 85 HP. at 3500 RPM. Allowing for the difference in mechanical efficiency between the two speeds, it is clear that our exhaust system should be increased about 75% in capacity if we are to have only the same percentage of power loss as previously. The downpipe loses some 4 HP at present. We therefore recommend that this should be made at least 2", actually 2 1/4" would be a better size if it could be brought in reasonably with the cast manifold. We do not want the front expansion box, we want the pipe to go straight through to the silencer. The main expansion box loses 10 HP. naturally we would like to increase its capacity in the same ratio as the power increase. The main difficulty being to fix the expansion box on the existing car. We consider that for the time being we had better experiment with this on our own until we get what we want. At the present time the swan-neck is a very serious loss to power, accounting for no less than 6 HP. We consider that this is most uneconomical way of obtaining silence, and we should open out to enlarged size that can be conveniently got in the space available, we suggest P.II dimensions. If we have the exhaust manifold downtake pipe and fish tail that we want, we should be reasonably well prepared for the new cast iron head. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||