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 report on modifications to the Paragonine carburetter, specifically testing the venturi tube.
| Identifier | ExFiles\Box 179b\2\ img213 | |
| Date | 19th December 1932 | |
| ORIGINAL R.{Sir Henry Royce} From He/Swdl.{Len H. Swindell} c. to SS{S. Smith} c. to Sg.{Arthur F. Sidgreaves - MD} c. to Gor. c. to Ry. c. to DA.{Bernard Day - Chassis Design} c. to WdW. He/Swdl.{Len H. Swindell}S/MA.19.12.32. X4027 PARAGONINE CARBURETTER. (LoG.3157). With regard to your query re. the venturi tube and its obstruction to the air passing from the outside we have tested out (LoG.3243). This is machining out the throttle body from 1.500 diam to parallel sides of 1.925 diam. Together with this the venturi is made parallel sided the internal diameter being .700 as before. These modifications increase the free area between the throttle body and the venturi from 1.17 to 1.37 sq. ins. and are to (Ex.9611 & Ex.9612). At the top speeds of 4500 R.P.M. and 3000 R.P.M. this increase in area made not the slightest improvement to the power or reduction in induction manifold depression. We have found that it is the suction piston which is the controlling feature of the air flow, for if the piston is completely removed even with venturi to LoG. 3157 the induction manifold depression is reduced from 2.5 ins. Hg. to 1.8 ins. Hg. The big advantage to the taper sided venturi is that it overcomes loading up after the unit has been running for some time at low speeds full throttle and the brake is released to a higher setting. It appears by this result, that the velocity of the flow through the venturi is reduced by the taper before entering the throttle body and none of the petrol falls back. With the parallel sided venturi the loading up is very bad even though we have drain holes for this purpose. | ||