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).
Page 2 of a report detailing engine modifications to improve performance, including changes to the transfer throat, exhaust valves, and water passages.
| Identifier | ExFiles\Box 123\5\ scan0280 | |
| Date | 1st February 1939 | |
| -2- account for such an alteration to the running of the engine, to quote, an "angel to a devil". This view was confirmed and was mainly found to be the reduction in transfer throat area, i.e. between the cylinder bore and the exhaust valve, effected by machining off the face, The modification FD.{Frank Dodd - Bodies}292, was then carried out whereby the transfer throat area was made as large as practical, this area being increased from 1.44 sq.in. to 1.64 sq.in., this effecting a considerable improvement, such that full power could be maintained, although with the ignition switched off the engine would run for 55 seconds before finally stopping. Sodium filled exhaust valves were then fitted and although no valve temperatures were recorded, the running after switching off was reduced from 55 seconds to 22 seconds for the unit to stop. By blanking up the 2 side holes .500 dia. thus making all the water pass through the water gallery feed jets and opening up several of the steam release holes between the cylinder block and the head from .187 dia. to .312, the time factor for stopping after switching off is in the region of 10 seconds and comparable with a Bentley V engine. We might mention that the reason for opening up the steam holes was the fact that the cylinder head gaskets were burning in a position where there were no normal sized water holes, namely at the forward end of the front combustion chamber, between Nos. 2 and 3 and the rear end of the rear cylinder. This modification reduced the burning of the gasket appreciably. Adhering to the switching off tests, additional water through the cylinder head, various types of sparking plugs and radiusing off the edges of the combustion chamber made little or no difference. In this condition we were able to take reasonable curves of power, both maximum and non-detonating, also sensitivity to ignition advance etc. which we describe below. All of the comparisons were carried out under conditions (a) Redline (No) fuel). (b) Test Bed exhaust system. (c) Sodium filled exhaust valves. (d) Mocked up Bentley V induction system 2 - 1 1/2" dia. S.U. carbs. (e) Modification to water holes previously described. | ||