Saw this Q/A about spark plugs in the Tech Correspondence section in the latest issue of Road and Track (Sept. 04), and thought it might be of interest for those of you with S/C motors. Especially if the illustration in the last paragraph of the answer describes a high RPM problem that you might be experiencing.
Question:
As a professional mechanic for over 20 years, I have seen hundreds of spark plugs fail due to carbon tracking, cracking or other problems with the porcelain insulators. With today’s incredibly powerful ignitions, I have seen plugs worn almost to a surface gap condition (.150-in. gap or more) where a new set of plugs made no appreciable difference to the running or gas mileage of the car.
My question concerns platinum plugs. They wear less, see an advantage in extended service intervals, but my view is that the spark plug inside the cylinder is responding to the demands of the engine, to the limit of the ignition system’s ability, and has nothing to do with the material in the electrode. Am I all wet, or would spark plug manufacturers be better off spending time on insulators instead of electrodes?
R/T Answer:
Given today’s arc-welder ignitions, getting a spark plug to fire is not such a struggle, as you’ve demonstrated. But sparking a suitably large flame kernel, and keeping it lit, in today’s often dynamic, high-pressure and lean cylinders is still a good trick.
So, yes, spark plug electrode material does not play a direct role in spark intensity. However, platinum and iridium electrodes can be made smaller, notably reducing misfiring because they result in more robust flame kernels. This is because the smaller electrodes are less of the shroud, exposing more mixture to the flame front.
An unusually dramatic illustration of this is with aftermarket supercharged engines running high boost. Such engines often falter at high boost and high RPM due to ignition failure. Simply screwing in iridium-tipped spark plugs typically eliminates the misfiring and allows the engine to rev to its power peak. In practice, this means a simple plug change is worth 30 bhp simply because the new plugs allow the engine to reach its designed redline.
Question:
As a professional mechanic for over 20 years, I have seen hundreds of spark plugs fail due to carbon tracking, cracking or other problems with the porcelain insulators. With today’s incredibly powerful ignitions, I have seen plugs worn almost to a surface gap condition (.150-in. gap or more) where a new set of plugs made no appreciable difference to the running or gas mileage of the car.
My question concerns platinum plugs. They wear less, see an advantage in extended service intervals, but my view is that the spark plug inside the cylinder is responding to the demands of the engine, to the limit of the ignition system’s ability, and has nothing to do with the material in the electrode. Am I all wet, or would spark plug manufacturers be better off spending time on insulators instead of electrodes?
R/T Answer:
Given today’s arc-welder ignitions, getting a spark plug to fire is not such a struggle, as you’ve demonstrated. But sparking a suitably large flame kernel, and keeping it lit, in today’s often dynamic, high-pressure and lean cylinders is still a good trick.
So, yes, spark plug electrode material does not play a direct role in spark intensity. However, platinum and iridium electrodes can be made smaller, notably reducing misfiring because they result in more robust flame kernels. This is because the smaller electrodes are less of the shroud, exposing more mixture to the flame front.
An unusually dramatic illustration of this is with aftermarket supercharged engines running high boost. Such engines often falter at high boost and high RPM due to ignition failure. Simply screwing in iridium-tipped spark plugs typically eliminates the misfiring and allows the engine to rev to its power peak. In practice, this means a simple plug change is worth 30 bhp simply because the new plugs allow the engine to reach its designed redline.
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