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).
Carburetion strategies for post-war cars, including induction pipes and a comparison of carburetter manufacturers.
| Identifier | ExFiles\Box 123\1\ scan0069 | |
| Date | 15th November 1940 | |
| To Rm.{William Robotham - Chief Engineer} from Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation} Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation}3/ET.15.11.40. CARBURATION. (Post War Rationalised Range) 1086 It is agreed that one of the more desirable points connected with our post war cars, especially the smaller ones, will be fuel economy. From our past experience on this subject, we know that to get this, the following factors must be combined:- 1. INDUCTION PIPE. The gallery bore to be a compromise between maximum top power and minimum wall deposition at low gas velocities. The latter can be subdivided into a compromise again between the gallery bore and the heat available to overcome wall deposition. 2. CARBURETTER. This instrument should be capable of supplying the correct mixture ratio for all working conditions. Stromberg and Zenith do this, but the S.U. does not. In the case of the latter, the S.U. Company have had numerous tries at making their carburetters fully automatic. They are a poor firm, however, at overcoming snags or improving their product. I cannot remember a single instance where the many alterations we have caused to be made on their carburetters and electrical pumps have not been due solely to our initiative and mechanical development. In other words we have had to tell them exactly what to do. The same can almost be said of Zenith, with the main difference that we do finish up with a fully automatic carburetter. The S.U. carburetter has another snag, inasmuch as its length on a small car causes a minimum available space for an efficient intake bend, and this is a snag as it is a very sensitive feature. We have been lucky in the past in only having to carburate a "six" with 2 carburetters. Under these conditions, the engine impulses are made to provide the part throttle weakening agent. But the intake bend and air silencer have to be combined with the necessary tests, otherwise the intake pipe can set up reactory forces which cancel out the part throttle economiser action. With a single S.U. carburetter on a "four", any automatic part throttle weakening is simply what you finish up with, and the camshaft is the only means of adjustment (after settling the issue with the air intake bend). | ||