Piston Slap: Platinum performance with Pertronix persuasion?
Regarding classic car engines that have a Pertronix electronic ignition inside the distributor, can they use platinum plugs after removing the points and adding electronic ignition?
I have a stock 1948 Plymouth six-cylinder and will be using Pertronix ignition in my distributor. Can I use platinum plugs, and what plug would you suggest?
I have a 1970 Dodge Charger with Pertronix, and I’m trying to figure out if I should use platinum, iridium, or just stick with copper.
Well, this is clearly a question on the minds of many a Hagerty Community member! But first, let’s get on the same page. Pertronix (and others, to be fair) allow classic car owners to retain the external look of their stock distributor, but with solid state internals like the ignition systems ushered into automobiles starting in the mid-1970s. And with it there was no more fussing with points of dubious quality, increased voltage, more reliable performance, and plenty of good vibes going forward.
Spark plugs are a little harder to describe, as their design is most differentiated by their longevity. When placed into a vehicle, a host of variables (ignition coil output, compression ratio, etc., and maybe even heat range) ensure they behave radically different. Most 1996-up vehicles are designed for platinum or even iridium plugs, and their ignition systems are sized up to provide the correct amount of juice to make them happy. I’ve personally seen a modern (modern-ish; it was a 2006 Crown Vic) vehicle absolutely murder a set of copper plugs in less than 30,000 miles. But I doubt the reverse is true, that older cars with a modern Pertronix ignitions must also use platinum or iridium plugs.
The answer, as per usual here at Piston Slap, is that it depends on your unique situation. The Pertronix Ignitor III puts out way, way more voltage than the baseline Ignitor system. And no matter the ignition system, platinum and iridium plugs may fail to perform to their maximum potential on an engine designed for copper plugs. So here’s what I recommend:
- For Bill: A 1970 Charger may need platinum/iridium plugs, if it has an aggressive ignition system upgrade, a built 426 Hemi with something like a 13:1 compression ratio, or forced induction, etc. If not, stick with copper.
- For Robert: This Plymouth is stock and likely has a baseline Pertronix Ignitor setup. Given that and the engine’s mild state of configuration, copper plugs are likely best.
- For Jim: This concern is more generalized, and there’s no better general advice than to stick with whatever the motor came with from the factory. (Which is usually copper.)
Considering most vehicles this age are not used for primary transportation, and since many have easy-to-reach spark plugs, sticking with copper spark plugs really isn’t a big demand to place on people. Their lower asking price is the textbook definition of an “added perk” too, but Piston Slap isn’t about my thoughts being final conclusions. This is only a means to encourage comments from readers.
So, as a member of the Hagerty Community, what do you think each of these guys should do?
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