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 performance, discussing compression ratios, detonation, and ignition characteristics for various car models.
| Identifier | WestWitteringFiles\Q\December1926-January1927\ 40 | |
| Date | 1st December 1926 guessed | |
| contd :- -3- Raising the compression ratio is probably one of the simplest ways of increasing our MEP - as previously demonstrated 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 standard 4.2 / 1 ratio engine. The engine was also 'livlier' than the standard product. We must 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 characteristics to the previous one tested in respect to the difference in the advance requiredbetween synchronised and single ignition. The spark advance necessary to give max. torque can be considerably 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 contd :- | ||