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, covering valve timing, ignition systems, and combustion chamber design.
| Identifier | ExFiles\Box 147\5\ scan0132 | |
| Date | 8th July 1937 | |
| -3- Rm{William Robotham - Chief Engineer}/CTS{C. Trot Salt - Carburation}11/R.8.7.37. It is one thing to obtain a uniform weak mixture setting, but there must be available at the same time a sufficiently high voltage to ignite these weak charges. We have proved that the present production coil is far below the standard of the Lucas or Delco in this respect. Valve Timing and Overlap. We know that overlap is the main controlling factor re slow running quality; and it also plays a big part in part throttle light load economy. Maximum accelerations are controlled at Vauxhall's by the design of the bottom tappet. Their maximum lift is also influenced to a large extent by valve spring behaviour. Our exhaust silencer losses at present are causing us to turn our attention from high speed power, in favour of middle speed power, even if we have to forfeit 10% top power. Ignition. As mentioned earlier in this report, any attempt at running on lean mixtures has, up to date, been made impossible by the failing of our ignition system to supply a consistently high enough voltage. Vauxhall's have experienced the same thing and got over the trouble in this way. They have an instrument which measures the maximum voltage required. Comparative tests can be carried out between different coils, plugs, wiring, etc., and finally a special coil has been produced which gives the necessary result by Lucas. Suction operated ignition worth 10% on Vauxhall cars. Combustion Chamber Design. In the design of their combustion chamber, Vauxhall's work on the principle that flame travel follows the same law as sound waves. In other words, as the flame front progresses from the position of the spark plug point, so the combustion chamber volume should increase in proportion. An attempt is already being made on our car single cylinder unit to follow this practice. We may be able to make a slight modification to our main engine cylinder head to conform more closely to this idea, as an experiment during our fuel economy development. | ||