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 harshness, its causes in the induction system, and improvements from vaporizer pipes and compression changes.
| Identifier | ExFiles\Box 19\7\ Scan071 | |
| Date | 9th November 1922 guessed | |
| -2- point than any American car, and was consequently run by most chauffeurs too far advanced for best power, but without showing much harshness in running. The 28 cu. in. engine requires more careful handling of the spark because of the greater tendency to chirp, but this effect is minimised by the automatic advance of the American Bosch battery ignition. The cause of harshness in certain engines, which we still meet with occasionally on test, we find to be in the induction system. Any engine which feels harsh when first put on the dynamometer is also found to load-up, and either a projecting fin will be found in the throttle or changing the induction pipe will rectify the trouble. The vaporizer pipe gives far more consistent results than before, but occasionally an induction pipe will be found which because of some internal fin or pocket, will cause loading. In every case, this tendency is first shown by a general roughness in running at speeds below 1000 r.p.m. We have tried the recommendation of deliberately leaving sharp corners at the induction pipe bends, and allowing the supply pipe to project 5/16" into the manifold, but did not find consistent results. Of six pipes, three were good and three loaded. The vaporizer pipes have been fitted to a number of cars with 28 cu. in. compression space, without alteration of the compression, and have improved the performance of these cars without causing roughness. The gas consumption has also been improved by the vaporizer pipes from about 9 miles per U.S. gallon to about 11, with a covered body. Summarizing:- We find the chief cause of harsh engines to be in the induction system, and to be a preliminary sign of loading. The spark cannot be much too far advanced with American gasoline because of chirping, except on the very low compression engines. High compression engines are not acceptable with American gasoline (especially in covered bodies) because of the booming noise produced in the body. Increasing the compression space by 1 cu. in. eliminates most of this noise. | ||