The new Autolite Platniums are sitting on the workbench waiting to go in. I'm running Petronix on my car 70 BOSS 302. What is the ideal spark plug gap to run. I have heard up to 45 is okay. What is the consensus?
I don't know if I agree with Steve. A friend of mine, who is very knowledgable in these things, told me that you could widen the spark plug gap when you installed a Pertronix unit up to .045" due to the lack of a condensor.
I widened the gap as my friend suggested, to .040" from .035" and it did wonders for my performance. Altohugh Steve is definitely right about one thing: A hotter coil needs a wider gap. I myself run a complete MSD system and I gap my plugs to .045" now.
If you develop a high speed miss at 0.045" then back it down to 0.040". I had one several years ago and it felt like fuel starvation. It was just the wide gap I set the plugs at after installing the Pertronix. I kinda' feel the Pertronix isn't really a performance part, it's more a convienience and reliability thing. I run them in both my cars!
i'm running a 68 302 in my 66 and i have the flamethrower coil in addition to the Pertronix unit. according to the documentation that came with my Pertronix unit it said you can set the gap .08 over the stock. IIRC the stock gap is .32, so another .08 gets you up to .40
i set mine at .40 after discovering the whole passenger side was gapped incorrectly. i cant attest to the effect because i developed an arc from the plug boot to the header pipe, so i need to put all new wires in and they wont be in until tuesday.
Pertronix ignition module change does not alter the fact that the coil remains the same and its still a conventional ignition system. In this case the gap does not change from factory specifications.
This situation is changed if the coil is changed or if the coil is triggered by an electronic control box (capacitive discharge ignition system). If the coil is a hotter coil, the gap can be increased modestly (widening it a bit can help with a hotter coil). If CD ignition, the situation is radically changed because a CD ignition can double or triple the voltage at the plugs. In this case, changing them to .045" or even .065" is not a problem as the output of CD ignitions is high enough and strong enough to jump this gap at any rpm.
You want the widest gap possible for the engine to fire reliably at all rpms so here's a guideline:
Conventional .035 is about tops
Hot conventional coil .040 is about tops.
CD ignition box .065 is about tops
If you have one system, don't want to change it and have grey to black plugs on examination, use one heat range hotter plugs (longer thinner center insulator).