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).
Summary of engine tests comparing aluminium and cast iron cylinder heads, focusing on temperature, pre-ignition, and compression ratios.
| Identifier | ExFiles\Box 19\7\ Scan137 | |
| Date | 21th April 1929 guessed | |
| contd :- -4- We have not been troubled with oil fouling the plugs on this engine so can therefore select a cooler running plug. SUMMARY. (1) We have shewn that the plug bosses in the alum. head are a slightly higher temperature than a similar position on the cast iron head. The highest temperature recorded on the alum. head was 215°C while that on the cast iron head was 212°C. Withdrawing the spark plug and providing better water passages round the boss as shewn on Lec.2689 should be a definite improvement in eliminating hot spots. (2) Pre-ignition occurs with the standard cast iron head when operating on a similar high compression ratio and using plugs (std. K.L.G.) but the trouble is nowhere near so obvious as with the turbulent head because there is little or no loss of power. (3) With the compression ratio of the alum. head reduced to 5.1 from 5.6 the engine will operate satisfactorily on similar sparking plugs which give trouble on the higher ratio. (4) We think a ratio of 5.25 : 1 should be satisfactory when used with the modifications shewn on Lec.2689 and more suitable sparking plugs. The clearance between the cyl. head and the pistons is .062" which is in the same order as used on Phantom. We have not yet obtained the complete curve of ignition advance required but approx. 35° advance is needed at a speed of 2500 r.p.m. Hs{Lord Ernest Hives - Chair}/A.C.Lovesey. | ||