FORMULA ONE TREND OF DESIGN

FORMULA ONE TREND OF DESIGN

Ignition Systems

THERE HAS always been variety in ignition systems for racing engines, different systems offering different advantages and appealing to individual designers or choice being affected by nationalism and industry. In the days of the racing magneto there were Lucas, Simms, Bosch, Duceflier, Scintilla and so on, each having its following. Just as the ignition system is a vital and important part of an engine, so the sparking plug is equally important and plug manufacturers invariably work hand-in-hand with ignition manufacturers. The magneto disappeared from the racing engine around 1959160 and as peak r.p.m. of racing engines increased coil ignition took over, starting as the simple electric coil and distributor and developing into highly sophisticated electronic equipment.

The igniton manufacturers were,.and still are always seeking to provide bigger and better sparks to fire the plugs as compressions and b.m.e.p. figures keep rising and American systems at Indianapolis led the field in ultra-high voltage. A point was reached where the normal single electrode sparking plug could no longer sustain those high voltages for more than a few minutes no a new type of sparking plug was called for. The high voltage ignition systems were known as capacity discharge and the special sparking plugs developed for use with this CD ignition were called surface discharge, or SD, Basically these plugs did away with the separate tag to which the spark jumped from the centre electrode on the normal plug. Instead the centre electrode discharged radially in all directions to the annulus of the outer body of the plug over the full 360 degrees, all at the sarne time, or to any particular point that happened to be nearer to the centre electrode or offering the best conditions for a spark to travel through. The CD ignition system and the SD sparking Plug eventually found their way to Formula One engines, and the Champion sparking plug people iv particular worked closely with the Italian Alagneti-Marelli firm on u system for the flat12 Ferrari engine. A variation on the

surface-discharge plug is the Semi-surfacedischarge plug, in which there is an annular air-gap between the insulator surrounding the central electrode and the outer body of the plug, the spark being able to traverse the gap at any point, radially from the central electrode. At the moment in Formula One the Magneti-Marelli CD ignition system is the most popular in use on Ferrari and Alfa Romeo engines. naturally, and also on the turbo-charged Renault V6. Of the Cosworth DFV users McLaren, Lotus, Ligier, Arrows and Osella all use Magneti-Marelli, while Fittipaldi use it on Wu of their engines, being unconvinced of its superiority to the orthodox Lucas coil system. On this Italian system there is no automatic retard mechanism to ease starting, though usually a DFV will fire up on fixed ignition advance. However, if it doesn’t go first time there is a “retard” switch in the system that can be pressed to delay the spark and give a retarded ignition firing point, the spring-loaded switch being released as soon as the engine fires. An advantage of the SD or semi-SD sparking plug is its ability to continue firing even when “wetted” by a rich mixture, so that mechanics love the system as it has done away with the bogy of “wetting all the plugs”. Known affectionately as the “lightning-voltage system” an engine that has got hopelessly rich with flooded injection trumpets can still be made to start without the necessity of removing and drying the plugs. A similar CD system has been developed over the last few years by Walter Scherhag, a German electronics engineer with a factory near Frankfurt. His firm is called Contactless Ignition and his first experiments with the Cosworth DFV were with Team Tyrrell in the days of the Project 34 six-wheeler. He was soon working closely with Cosworth Engineering and Champion plugs and today Williams, Brabham. Tyrrell and ATS all use Contactless ignition on their engines. While developing the ignitiog system Scherhag also perfected a vastly superior “rev-limiter” to the Lucas one normally used on Cosworth engines. Teams have found that the Contactless “rev-limiter” is much more consistent in its ability to “fade” the ignition at a pre-set figure. Today’s Cosworth V8 engines are limited to 10,800 r.p.m. and the latest engines. with larger diameter valves, known as “big valve Cosworths” are rather critical on peak r.p.m. All the teams using the Contact less ignition system praise the “rev-limiter” and its ability to remain constant,

whereas the Lucas system has been known to vary over IWO or three hundred r.p.m. At today’s cornering speeds the driver has little time to actually “read” the tachometer on gear changes and relies on the “rev-limiter” to tell him when to change gear.

As the name of the German firm implies there are no orthodox make-and-break ignition contacts in the system, nor in any other racing ignition system these days, the pulses being effected by a “trigger” pick-up against terra tines on the flywheel onus a rotating disc, or as in the case of the latest Cosworth engines, off the nose of the crankshaft. This is the most satisfactory place to take your “pick-up” from as it is compact and suffers no variations due to back-lash in gears as you get if you take it from a camshaft or a distributor disc.

The third system in use is the normal Lucas coil system as developed for the Cosworth VS, but only the Ensign team use this English system exclusively. Fittipaldi use it on half their engines, unable to convince themselves of any advantage or disadvantage over the Magneti-Marelli system. The Lucas is not a capacity discharge ultra-high-voltage system, so it uses normal sparking plugs.

Some drivers who have tried Cosworth V8 engine with Lucas ignition against engines with Magneti-Marelli or Contactless CD ignition and SD plugs. feel that the latter system gives better torque characteristics. What is probably happening is that the SD plugs are working better at lower r.p.m. when the injection mixture is not perfect, probably too rich after being on the over-run, so the feeling would be that the CD ignition is giving “pull”. Actually it is the surface-discharge plug that is better, hut it needs capacity discharge ignition to make it work. It is a “chicken-and-egg” syndrome.

There is no doubt that the general trend has been towards CD ignition, with Magneti-Marelli the favourites. Their technical assistance during practice and testing encourages this, while Walter Scherhag is making big strides with his Contactless firm and working closely with the teams. Lucas seem to be falling by the wayside, not through lack of expertise or enthusiasm in the racing division, but from apparent apathy in the hierarchy. It seems that “management” cannot, or will not, see the value in Formula One racing.

D.S.J.