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).
Report comparing performance and petrol consumption for Twin S.U. and Duplex Stromberg carburettors on a B.60 No.4 engine.
| Identifier | ExFiles\Box 123\1\ scan0010 | |
| Date | 27th December 1939 | |
| Rm{William Robotham - Chief Engineer}/ym.2/JH.27.12.39. CARBURETTER TESTS ON TWIN S.U. & DUPLEX STROMBERG CARBS. We have just completed a series of performance and petrol consumption tests on B.60 No.4. Cast iron engine unit fitted in 3.B.50. car, with Twin S.U. carbs. and the Duplex Stromberg carb., the S.U. carbs being 1.50" dia. fitted to a 1.50" bore induction pipe, and the Stromberg a 1938 Cadillac model fitted to a 1.750" bore induction pipe. The engine had fitted the original high power head EB.3844, with a throat area of 1.44 sq.ins. and a comp. ratio of 6.25 : 1. For record purposes of performance it should be noted that the engine-road wheel ratio was 2800 engine rpm. at 60 mph. with 6.00 x 17 tyres fitted at 35 lbs.sq.in. pressures and the weight of the car was 38 cwts. 3 qrs. 14 lbs. With the Stromberg set up as stated above, we could not obtain such good slow running as with the Twin S.U.'s and we intend to try a smaller bore induction pipe of 1.50" dia. From the attached graphs it will be seen that the Twin S.U. Carbs give a better road performance than the Stromberg, although the BHP. curve does not show any advantage. Our method of taking acceleration figures is to bang open the throttle to full throttle at 5 mph. in top gear, and start a stop watch as the speedometer finger passes the 10 mph. line, and stop the watch as the finger passes the 20 mph. 30 mph. 40 mph. line etc. This records the Graph Text: MPH SECS Legend: A - TWIN Su's B - DUPLEX STROMBERG C - TWIN Su's AND TWIN EXHAUST SYSTEM Table Data: MPH, A, B, C 10, 4.0 SECS, 4.1 SECS, 3.9 SECS 20, 8.0", 8.5", 7.4" 30, 12.3", 13.1", 11.8" 40, 17.63", 18.55", 16.6" 50, 24.4", 26.35", 22.56" 60, 35.0", 37.0", 30.22" | ||