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).
Technical letter detailing engine displacement figures, carburetter settings, and manifold design.
| Identifier | ExFiles\Box 122\1\ scan0034 | |
| Date | 3rd December 1928 | |
| OY3.R.12.3.28 - 5 - December 3rd, 1928. This car has engine displacement 195.6 cu. ins. Compression Ratio ----------- 5.2 Displacement per foot--------- 67 cu. ins. Displacement per ton foot----- 44.5 cu. ins. (for 4 door sedan wt. 3000 lbs.) Against the 20 hp., Eng. disp-----191 cu. ins. Disp. per foot---------------- 56.5 cu. ins. Disp. per ton foot (3600 lbs)----- 31.5 cu. ins. As a concession to the weight of the 20 hp., a 1-1/4" carburetter is about the maximum which they would recommend. Print SK-229 showing comparison of cars is attached. Setting. The carburetter setting which we have arrived at is :- Main Throat ---------------- 1-5/16" Main Jet ------------------- #34-4 = .111" and .209" dia. Compensating Air Bleeder--------- #59 = .041" dia. Main Restriction (High speed needle) 2-3/4 turns open. High speed needle seat drilled----- #38 = .1015" dia. Economizer Restriction----------- .037" dia. Accelerating pump stroke--------- Full stroke Accelerating jet --------------- #70 = .028" dia. Pump stud drilled with two holes #60 = .040" Throttle valve------------------- 21° The carburetter which is being sent to you is set/this way. The weight of the carburetter complete without air cleaner is 9 lbs. and the cost about $14. Manifolds. In connection with my note OY1.R.11.28.28 suggesting resonance effects in the manifold, we have taken rough dimensions of the Packard 8 manifold, which represents practically the present standard type of American manifold. This is shown in SK-264. The intake and exhaust manifolds are cast in one piece of cast iron, vitreous enamelled for a finish. There is no exhaust choke valve, the hot spot jacket being part of the exhaust manifold. There is no vertical pipe, the carburetter being bolted direct to the underside of the hot spot. The inlet manifold is rectangular section with the long side horizontal. Distribution, to judge by the even heat of the engine, is very good. Possibly this type of manifolding avoids resonance effects. It certainly cleans up the side of the engine and make tappets accessible. Very truly yours, Maurice Olley | ||