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).
Comparison of SU and Stromberg carburettor characteristics, discussing performance, simplicity, and tuning.
| Identifier | ExFiles\Box 147\5\ scan0192 | |
| Date | 4th September 1941 guessed | |
| 3. It therefore follows that it may stand considerable weakening off before the limit is reached for this particular air temperature. Weakening off should really be taken to the limit to provide a true comparison with the Stromberg unit. By its very design the S.U. must beat the Stromberg in cold weather if an impact exhaust hot spot is not used, because with an expanding carburettor the induction pipe depression is greater during pick up, thus increasing the volatility of the fuel. This effect is, of course, increased by the hydraulic piston damper. 2. The carburettor is simple, cannot easily go wrong, and is nothing like so susceptible as the Stromberg to dirt in the petrol. 3. The carburettor cannot be set with any certainty on the road. This is because the same needle has to do the metering at full throttle and part throttle. Full throttle ideal metering may be obtained on the road, but the part throttle economy is generally obtained by modification to the induction pipe to take advantage of pulsation - Again taking the long view this is not a disadvantage, but it can be seen that before one is sure that an S.U. setting is unquestionably the best possible for any particular | ||