Question: I have a 64 Thunderbird with a rebuilt 390 (stock) with aftermarket intake, carb, and cam. I read a post somewhere that adding a high-voltage coil can cause the spark to jump and thus burning a hole in stock pistons. The idea is that the engines were not designed to handle more than 30,000 volts. I just want to know if anyone has an opinion about this? Do you agree with this assessment?

I can’t see why an arc would prefer to jump a relatively large distance to a piston top that’s not as well grounded as it would to the small distance to the perfectly grounded spark plug tip. Absolutely not. Spark gap is generally .035-.045″. The distance from the end of the plug to the piston top would be at least 4-5 times that in a stock engine. Can you imagine an engine running with a spark gap of .5″? It would take a heck of a lot more voltage than 30K, and a missing electrode, to create a spark like that. I’m not an electrical engineer, so I can’t explain the exact theory behind it. But I am a car guy, so I can explain the application. Your secondary ignition system will create as much spark as the engine requires, regardless of what it’s capable of. If you have good fuel, low compression, low rpm’s, and a small plug gap (like .035), you don’t need a whole lot of energy to make a good spark. Say 10K volts. So that’s all it makes. You may have a 50K coil and 10mm wires, but you’ll still only make 10K volts, because that’s all it needs. Now, start adding things that make a spark more difficult to generate – like nitrous, high compression, high rpm’s, etc. Now that high powered ignition system comes in to play. The engine needs 50K volts to generate a spark, so it better be capable of that.

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