Present-Day Racing Car Spark Plug Design
Although spark plug operating principles are the same whether in racing cars or in the family saloon, it stands to reason that Formula One racing engines turning over at 10-12,000 r.p.m. have much more demanding operating requirements.
So many Grands Prix have ended with only a handful of cars left to finish, that it has been asked whether spectators are getting their money’s worth out of motor racing. Seldom, however, is retirement due to spark plug failure, and it is interesting that such faultless performance has been attained while spark plugs have become so much smaller. Engines being now so complex and yet compact, the necessity for maximum valve area and their configuration leaves only very limited space for the spark plug which in most Formula One engines is only to mm. dia. thread and ¾ in. reach. Whereas there were originally two valves in each cylinder or sometimes three (twin inlet and single exhaust), the latest Formula One engines are now mostly built with four valves per cylinder—two inlet and two exhaust.
Even though during the last decade the specific output of racing engines has increased considerably through these breathing refinements, greater compression ratios and higher engine speeds, no longer is it necessary to warm up racing engines on “soft” plugs and then change them to “colder” plugs for the actual race, with the attendant risk of mistakes in the last minute panic when if a “sort” plug was accidentally left in, the dire results of pre-ignition and holed pistons soon put the competitor out of the race. Heat ranges have been so widely extended that the Champion Company are now able to cover the requirements of all of the 1968 Formula One engines with just two types of their GR range 10-mm. spark plugs. The G-59R is used in the Brabham-Repco, B.R.M., Ferrari and Eagle Weslake 3-litre V-12 engines. Because of variations in engine design and operating characteristics such as the position of the spark plug in the cylinder head, turbulence factors of the incoming fuel/air mixture, etc., the slightly-colder G-56R is more suitable for the Cosworth 3-litre V-8 (McLaren-Cosworth), and Honda 3-litre V-12.
Design development is largely accomplished by means of a special thermo-couple plug originated by the Champion Company’s engineers, in which tiny wires threaded through microscopic holes in the insulator enable actual working temperatures at various points in the spark-plug insulator to be accurately measured by electrical recording instruments. This ensures that plugs chosen for a particular engine application operate well below dangerous pre-ignition levels and further gives a measure of the allowable ignition over-advance before this is likely to occur.
For years it was accepted that the wide operating requirements in racing demanded silver or other equally exotic alloy electrodes, but with advances in general design, champion cover the same racing heat range using the same special nickel-alloy electrodes as on their standard car plugs. Considerable investigations have also been conducted into insulator strength which has to take care of greater dynamic stresses, encountered at higher engine speeds, as well as resultant overall variations in thermal stresses. While one end of the spark plug is subject to under-bonnet temperatures around 100ºC., the firing end has to withstand temperatures alternating rapidly between combustion heat around 1,500ºC. and the near-freezing mixture intake. At 8,500 r.p.m. the cycle of these temperature stresses is taking place some 70 times per second.
An important part is played by Champion’s own particular method of sealing the electrode into the insulator and between insulator and plug shell, this “labyrinth” seal having proved to have substantial advantages in highly-stressed racing applications against other conventional methods. Advanced shell materials also help in this respect. Improvements are constantly being made in the dielectric strength of spark plug insulators, dictated by up-lifted voltage-availability, and plug voltage requirement. All these factors account for the unique features of the Champion insulator, the most sophisticated part of the spark plug, the material specification for which is extremely exacting. The physical strength of the Champion insulator is such that using a direct loading force its nose can be forced through a ¼ in. mild steel plate without fracturing.
Observant spectators around the pits are sometimes liable to get the wrong impression during a race, when they see a plug being removed from a car that has just pulled in. This does not necessarily mean plug trouble, but it is a regular practice since experts can quickly diagnose things that are happening inside the engine simply from the appearance of the plug firing end, so long as the driver cuts the engine at full throttle before coasting in. The spark plug is the expert’s “hidden eye” and helps in establishing optimum fuel/air ratios, ignition settings, mixture mal-distribution, excessive oil consumption and a host of other engine situations. It follows that all this technical know-how derived from racing ensures that the Champion spark plugs fitted by most manufacturers in every-day cars are of the highest quality.