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 road wheel horsepower, speed, and the effects of exhaust cut-out and vehicle windage.
| Identifier | ExFiles\Box 24\5\ Scan094 | |
| Date | 4th July 1925 | |
| -2- The peak of the road wheel H.P. curve with the cut-out closed is passed at 60 m.p.h. and after this point the H.P. available commences to fall off. When therefore the windage of the car is reduced raising the max. speed, the actual road wheel H.P. available to produce this higher speed is less than before. Thus these figures tend to belittle the effect of reducing the windage of the car or opening the cut-out. A point of interest is that fitting side curtains with the hood up actually reduces the windage of the car. The hood alone is responsible for a drop of 3 m.p.h. in max. speed. Superficially opening the cut-out does not seem to give the increased speed one would expect. A close investigation of the figures obtained in dynamometer and tractive resistance tests, indicates however, that this result is approx. correct (See Graph 1. curves A.{Mr Adams} B. and C. Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}4.7.25.) | H.P. available at road wheels. | Road speed. | Increase in vel. due to increase in H.P. | |---|---|---| | C.O. closed. | 68 H.P. | 74.5 | | | C.O. open. | 73 H.P. | 76.5 | 5 HP. increase equivalent to 2 m.p.h. Curve Graph I | Undoubtedly on the track the impression with a free exhaust is rather of much better acceleration from 50 to 70 m.p.h. rather than a great increase in max. speed. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} | ||