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 engine performance relating to choke area, carburetter restrictors, and induction pipe depression.
| Identifier | WestWitteringFiles\T\November1928\ Scan012 | |
| Date | 1st November 1928 guessed | |
| contd :- -2- a free choke area of 1.53 sq.ins. gave low induction pipe depression and consequently good power, with the maximum of suction at the choke. The minimum free area through the expanding carburetter with the restrictor in its lowest of fully withdrawn position is approx. 1.2 sq.ins: and this we think accounts for the high depression. The fact that greater surface area is exposed for this annular form of choke than with the usual choke and central diffuser may result in a smaller orifice coefficient and so demand an area in excess of 1.53 sq.ins. in order to give the required power output. When the engine is run at full throttle we find the restrictor reaches its lowest or most withdrawn position at 1000 r.p.m. A stiffer spring to permit the restrictor not being fully withdrawn before say 2500 r.p.m. would naturally result in still higher manifold depressions. We took a snatch reading of the power and depress- ion at 2000 r.p.m. with the restrictor completely removed and found the depression on the induction pipe was 1.1 ins. mercury and the power approx. the same as with the RRCH and 1.53 sq. ins. choke. The power would have been better but the engine did not run well due to a weak mixture, it being impossible to richen up sufficiently with the restrictor removed. In order to run the carb. without the restrictor - to prove the choke is then sufficiently large - we shall blank some of the air holes in the emulsion tube. We propose to make some experimental restrictors contd :- | ||