Engine performance comparing standard and long-duration camshafts, discussing power curves, B.M.E.P., and valve bounce.
| Identifier | ExFiles\Box 102\5\ scan0003 | |
| Date | 31th March 1927 guessed | |
| contd :- -2- previous best results obtained with the standard camshaft. The carburetters used were two new Zenith triple diffusers similar to those employed on the Lorraine Dietrich but slightly larger chokes were fitted resulting in a lower induction pipe depression. Consequently in order to afford a true comparison between the two camshafts another power curve was computed from that given by the standard camshaft in order to reduce both tests to the same induction pipe depressions. It will be noticed that the power curve is still rising at 3000 r.p.m. but at speeds in excess of this we were troubled with valve bounce which naturally adversely influenced the power. For the purpose of exploring above this speed we are making some valve springs giving higher pressures. At 3000 RPM. the gain in power due to the camshaft alone is 15.5 HP. or 22%. The B.M.E.P. curve reaches a maximum value of 124.3 lbs/sq.in. at a speed of 2500 r.p.m. whereas the previous best results with the std. camshaft gave a max. of 120 lbs/sq.in. at 1750 r.p.m. At the lowest speed shewn on the curve - 750 RPM. - the B.M.E.P. is 3.48 lbs/sq.in. lower with the long duration cams or approx. 3%. It therefore seems reasonable to suppose that with a camshaft possessing this characteristic the compression ratio could be increased by an amount to restore this low speed torque without increasing the tendency to detonate and at the same time result in still more power at the high speeds. Previously - on the standard engine - we have been somewhat limited in raising the compression ratio because of the increased tendency to detonate. This point however will receive further investi- gation. contd :- | ||
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).