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).
Engine detonation tests comparing different cylinder head materials, valve types, and ignition settings.
| Identifier | ExFiles\Box 134\2\ scan0136 | |
| Date | 23th August 1937 | |
| -2- It appeared, however, unaffected by - (i) Compression ratio up to 6.8. (ii) Ignition advance within very wide limits. (iii) Type of plug used. (iv) Cylinder head material. It was found that high speed detonation could be eliminated by using a cast iron head and block, with a throat area of 1.16 sq. in., and a stem-cooled exhaust valve, this latter also appearing instrumental in lowering the low speed detonation intensity. Fig. 2 gives curves. Due to the obvious disadvantages of using a salt-cooled valve, another head was tried (No.4) inclining the inlet valve, and employing a throat area of 1.57 sq.in., the head material being aluminium. This was first used with an aluminium block with a dry liner and an uncooled exhaust valve. High speed detonation was completely absent, and the low speed stuff quite moderate. These results were borne out when a cast iron block was fitted with this head, the high speed detonation still being absent with a solid exhaust valve. These tests were run on an aluminium gasket which had been proved inferior to both corrujoint and C. and A.{Mr Adams} It is clear, therefore, that the inclined valve head, when used with a C. & A.{Mr Adams} gasket, 6.4 C.R. solid exhaust valve and cast iron block will give satisfactory results as far as detonation is concerned at high speeds. (3) IGNITION ADVANCE. On the original No. 1 head, the ignition advance necessary for maximum power was found to be considerably less than the standard Bentley. Taking ignition advance as a criterion of engine smoothness, it was thought that this head might prove rather rough, unless an ignition curve approximating to that of the Bentley could be obtained. Fig. III shows the gradual improvement effected from the original cast iron head to the final inclined valve alum. head, which gives a curve extremely close to standard Bentley. (4) PLUG POSITION. | ||