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).
Preliminary tests on twin S.U. carburetters for the Peregrine engine.
| Identifier | ExFiles\Box 31\5\ Scan034 | |
| Date | 20th March 1933 | |
| Files. XN87 20.3.33. XU87? TWIN S.U. CARBURETTERS ON PEREGRINE. We have made preliminary tests with two 1 3/4" dia. S.U. carburetters on Peregrine with an Induction system scaled down from Bensport. The two halves on the induction have been balanced the balance passage being .375 dia. and in proportion to Bensport which is .500 dia. on a 1.500" dia. pipe, the pipes used on Peregrine being 1.125 dia. The balance passage is 1.500" long and makes the overhang from the centre ports approximately one-third the port dia. which is also proportional to Bensport. The carburetters have been placed between Nos. 2 & 3 cylinders on the forward-pipe and between 4 & 5 on the rear pipe. The distribution so far is the best we have had on Peregrine and compares favourably with Bensport although there is a tendency for the centre cylinders to richen up at low speeds. We have not completed our tests at present as we may have to increase the size of the balance passage in order to overcome induction roar, this may also influence the distribution but until we have tried the increased size we cannot say exactly how much affect it will have. Attached are metering curves with the only suitable needles we have, actually we appear to want a cross between the AH.2, needles and 5" needle. The air valves were only lifted .645 at 4500 r.p.m. and the maximum lift of the is 1.125 so that the carburetters appear to be too large; the induction pipe depression is approximately 1.2 to 1.3 at 4500 r.p.m. Smaller carburetters are worth trying as we may improve the distribution still further. The distribution at the top speeds appears to be affected by too much heat, but for slow running we want all the heat we can get, there was an increase at the top speeds of 1.5 HP. with no heat to the hot spots, but considering the short periods of time that the engine is running at 4500 r.p.m. on the road it is questionable whether it would be worth our while to reduce the hot spot temperature at the expense of the slow running. The slow running is by far the best we have yet, the engine maintaining an even 250 r.p.m. for one hour. R.Matthews. | ||