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).
Increasing Mean Effective Pressure (MEP) by testing a new engine head, detailing compression ratios, detonation, and ignition characteristics.
| Identifier | ExFiles\Box 42\4\ Scan052 | |
| Date | 10th December 1926 guessed | |
| contd :- -3- the simplest ways of increasing the MEP - as previously demon- strated on the 20 HP. and Phantom - the blue sports 10-EX, but we have been limited in this direction by the increased tendency to detonate. The new head, after the bench test, was fitted to car 14-EX and gave a compression ratio of 4.66 to 1 as the pistons on this engine had .128 head clearance. From road performance it seemed particularly good but detonation was reported to be a little more evident than on the std. 4.2 to 1 ratio engine. The engine was also 'livelier' than the standard product. We mu-st not adhere too rigidly to this first impression re. detonation because the ignition relay which was fitted gave the range required by a standard engine which, as we shew later, is earlier than required for this type of head. IGNITION CHARACTERISTICS. This head - LeC.2230 - displays similar character- istics to the previous one tested in respect to the difference in the advance required between synchronised and single ignition. The spark advance necessary to give maximum torque can be consid- erably reduced by using synchronised ignition - see appended curves on sheet 4. It will be noted the power output shewn on these curves is a little higher with the synchronised than with the single ignition, but this is small and only amounts to 1%. A point of importance shewn by these curves is the comparative lateness of ignition which can be employed when synchronised without appreciably reducing the B.M.E.P. In the example given at 1000 r.p.m., we could reduce the spark contd :- | ||