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).
Engine tests comparing valve lift and camshaft designs for power efficiency.
| Identifier | ExFiles\Box 182\M19\ img214 | |
| Date | 6th August 1931 | |
| -2- It will be seen from the above tabulated figures that the valve area and lift are relatively very much the same for both engines. We carried out some tests on the 25 HP. unit with a view to determining the optimum valve lift for efficiency. Curves II and III show the power gain resulting from increasing the lift ratio from .255 to .292. We should expect a greater gain with a long duration shaft and single low depression carb. It would appear that we can gain power up to a ratio of .3, it will be noted from the attached tabulated list that this is about the ratio used on the aero engines. The advantage in gaining power by increasing the valve lift is that no M.E.P. is lost at low speeds. However, for the same valve lift ratio China is still better off than the P.II and we are making some tests to see if we can get an improvement by clearing the head away experimentally round the inlet valves this being the alternative to high-lift. We have done this on some 2" inlet valves we had in a head and it gave improved results but may not do so with the std. valves. We shall carry out a test with the angle between the cams altered to 114° and the inlet opened 7° earlier as you suggest, also with a 5.25 - 1 C/R.{Sir Henry Royce} head. We believe that we might get slightly better results using two inlet cams rather than with the existing inlet and exhaust, as tests with the R.{Sir Henry Royce} engine cam forms indicated that we could reduce the exhaust duration to about 240° without detriment. Exhaust durations of much over 240° appear to be detrimental with any considerable back pressure such as we are bound to have to get silence. The slow running with the LeC.2918 camshaft seems quite satisfactory. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} Attachments. Tabulated list. 3 prints. | ||