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Old 09-25-2010, 05:31 PM
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Spark plug question

I bought a car with a 1960 390 Cadillac engine. The plugs are a little sooty (black,but dry) so I thought maybe I would go with a higher heat range. The book calls for AC 44 so I bought AC45. BUT the plugs that are in the car are Champion RJ12YC which does not cross reference with AC44. AND the champs have a longer reach electrode. I'm wondering if this longer-style plug was used for a reason,or just a mistake--Would there be any advantage using a longer reach plug?

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Old 09-25-2010, 05:57 PM
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Originally Posted by yragat
I bought a car with a 1960 390 Cadillac engine. The plugs are a little sooty (black,but dry) so I thought maybe I would go with a higher heat range. The book calls for AC 44 so I bought AC45. BUT the plugs that are in the car are Champion RJ12YC which does not cross reference with AC44. AND the champs have a longer reach electrode. I'm wondering if this longer-style plug was used for a reason,or just a mistake--Would there be any advantage using a longer reach plug?
I think I might begin by correcting the problem, too much fuel into the motor. Carburetor needs to be rebuilt, float level and float drop set and fuel pressure checked. What carb is on the motor?

Extended TIP plugs might aid combustion. They won't hurt anything, but be cautious that you don't use a plug with longer THREADS inside the chamber. The threads can glow red hot from the heat of combustion and light off the incoming mixture before the spark plug fires, causing detonation.
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Old 09-25-2010, 06:17 PM
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The car has 6 97s on it,but runs off the 2 center ones only---thought I'd mess with them over the winter. the plugs that are in it has the same amount of thread. So are you saying that the longer tips might be better for now? Or should I put the AC's in or just clean up the Champions?
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Old 09-25-2010, 07:17 PM
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Originally Posted by yragat
The car has 6 97s on it,but runs off the 2 center ones only---thought I'd mess with them over the winter. the plugs that are in it has the same amount of thread. So are you saying that the longer tips might be better for now? Or should I put the AC's in or just clean up the Champions?
I'm saying that you should stop trying to crutch the whole mess and fix it. You didn't mention the carb setup when you originally posted, but I'll bet money that the jets are too big and the fuel pressure is way too high. Those old carbs begin blowing fuel past the needle and seat at about 3 psi. Rebuild the carbs, lean the jets, get the pressure under control, then worry about spark plugs.
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Old 09-25-2010, 07:36 PM
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