Quote:
a cooler plug can greatly reduce or eleminate spark knock without any other adverse effects unless the plug heat range gets too cold.
Agree, it is always good science to eliminate the plug itself as the source of ping ignition. In a standard-shift performance car which gets revved up regularly, one heat range colder is standard.
As we've mentioned here and on some other threads, it is not so easy these days to know exactly what plugs are right for a TwinUltramatic Packard.
Today's unleaded gasahol and additives have made all our hard-won plug reading experience obsolete. Just listen carefully and make sure a colder plug doesn't make it go from pinging to missing.
Today's fuel will also "cold-foul" plugs if they aren't running hot enough. I had a customer bring in a car which wouldn't start. The float had stuck and filled the manifold with fuel. After we fixed the float, it still wouldn't start. The plugs were new, looked perfect, would jump a nice spark when tested out of the car. I worked most of a day replacing other ignition components. Finally, I installed new plugs and it ran perfectly. The old plugs looked and tested OK, but they wouldn't hit a lick in the engine under compression. From then on, if I have a missing engine, first thing I do is replace all the plugs with one heat range hotter. If new plugs fix the problem, it is the least expensive part on the car.
jack vines
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