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).
Tests of turbulent cylinder heads and ignition governors on Bentley and 20/25 models.
| Identifier | ExFiles\Box 82\4\ scan0321 | |
| Date | 10th June 1936 | |
| -2- As far as the Bentley with the turbulent head goes, these tests were merely a check to show that the Governor on this car is approximately correct. When we come to the turbulent cylinder head with the lip removed, in order to get the full benefit of smooth idling we require the ignition timing under these conditions to be something less than 5° before top dead centre on the Bentley, and less than 10° before top dead centre on the 20/25. The ignition advance curve must rise swiftly from this point to give satisfactory pick-up. The Rolls-Royce ignition governor is not good for getting a rapid movement at low speeds; in fact, it is almost impossible on production to make these governors start advancing at 300 r.p.m. with any degree of reliability. The Delco seems to get off the mark better under these conditions. In the case of the 20/25 with the deturbulated head, we think we can get away for the time being with a Rolls-Royce governor, though we shall have slightly more ignition advance when idling than might be considered desirable. In the case of the Bentley, however, the Delco gives us what we want We have a cylinder head and governor ready to be sent out to 22-S-V.{VIENNA} In the case of the Bentley, the deturbulated head and governor will be fitted to 6-B-IV. A curious feature on removing the turbulent lips on the Bentley, is that we pick up more than 10 H.P. at 4,500 r.p.m. This is rather surprising, but it has been checked a number of times. It would appear that the large inlet valves on this head are being masked by the turbulent lips. Briefly, these tests hardly justify the use of the turbulent lip on our cylinder heads, particularly on the Bentley. In our opinion, the almost insignificant reduction in detonation at the lowest speeds which is brought about by these turbulent lips is more than offset by increased roughness and loss of top speed power. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} Att: Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}21/KW.9.6.36. Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}22/KW.9.6.36. Hs{Lord Ernest Hives - Chair}/Syn. 23/KW.9.6.36. | ||