318 Spark Plug Gap?

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Robert Sweeney

Robert Sweeney

1966 Plymouth Barracuda
Joined
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Georgia
what would be the suggested Spark Plug Gap for a lightly modified 318?

Has an upgraded Cam (previous owner installed, brand and specs unknown) Holly Carb, HEI distributor, using Royal Purple HPS 10w40, and currently running E3.46 spark plugs.
 
Stock gap is .035. With HEI you could gap them at .040-.045. Remember, the gap increases as they wear. Personal preference but I won't run E3's.
 
toolmanmike said:
Stock gap is .035. With HEI you could gap them at .040-.045. Remember, the gap increases as they wear. Personal preference but I won't run E3's.
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Thank you! What plugs would you recommend over E3’s? I’m newer to N.A. Engines coming from forced induction. Not up-to-date on specifics. Always open to discussion that could improve my vehicle.
 
Champion. I think the correct number is RN12YC. Whatever the book says for that year 318.
 
Robert Sweeney said:
Thank you! What plugs would you recommend over E3’s? I’m newer to N.A. Engines coming from forced induction. Not up-to-date on specifics. Always open to discussion that could improve my vehicle.
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Spark plug recommendations are like opening up a can of worms. I have never had an issue with Champions. Others will have differences of opinion.
 
toolmanmike said:
Spark plug recommendations are like opening up a can of worms. I have never had an issue with Champions. Others will have differences of opinion.
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A TON of races have been won with Champion and Mopar. Whenever I hear someone bashing Champion plugs, I just put them on the "ignorant list" and move on.
 
Ive been a Dyno Tech for 35 years for one of the big 3. This is normal everyday stuff. Glad I could help.
 
Come to think of it, I believe all the historically important Mopar races were won with Champions.
 
Champion spark plugs and Mopar go together like peanut butter and jelly! They've come from the factory with them pretty much forever so what does that tell you? I've never had nothing but good luck with them so if it ain't broke don't fix it! But that's just my own experience!
 
Robert Sweeney said:
what would be the suggested Spark Plug Gap for a lightly modified 318?

Has an upgraded Cam (previous owner installed, brand and specs unknown) Holly Carb, HEI distributor, using Royal Purple HPS 10w40, and currently running E3.46 spark plugs.
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.045 seems right imo.
I know chevy uses .045-.050, chevy style ignition would make sense to stay in that spec.
@RustyRatRod
Ignorant? Hey let's not let our brand loyalty lead us to insulting others here, we arent ignorant...we know you like that big cam sound you get when your champions insulator falls out and starts to miss. Not fooling no one.lol
 
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I once had an 80 firebird esprit with the gutless and nutless buick V6 with factory HEI and superlight hydramatic three speed. I don't know what was different in the ignition to that particular engine but the spark plug gap spec was an .120 or .125 inch gap. I know, a full eighth inch! I don't think top fuelers use that much gap, and their mag systems have the output of an arc welder. Had factory high voltage warning stickers anywhere near the distributor. The only thing that could have helped that car was a good early seventies 350 Olds engine.
 
FWIW... I found out long ago that there ARE differences in plugs. My 10.3 SCR 351C would do fine on Champions and I'd get 10k miles or more on them before they would literally 'wear out' with the high temps eroding the electrodes. Autolites would last <5K miles and their electrodes would be eaten alive if I kept them in that long.
 
My Champeen coppers have been in there since 1999, sparked by a Big yellow SuperCoil.
I was gonna change them in 2004 the last time the engine was freshened, but they looked so good, I left them in there. The new replacements I bought are still in the trunk. The car went 93 in the Eighth on those ancient plugs, in summer of 2004. Cheapest plugs I ever bought. I haven't even looked at them since 2004.
Your results may vary,lol.
 
RustyRatRod said:
A TON of races have been won with Champion and Mopar. Whenever I hear someone bashing Champion plugs, I just put them on the "ignorant list" and move on.
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Mopar plugs are champion. Save the money unless you have a points car.
 
MOPAROFFICIAL said:
.045 seems right imo.
I know chevy uses .045-.050, chevy style ignition would make sense to stay in that spec.
@RustyRatRod
Ignorant? Hey let's not let our brand loyalty lead us to insulting others here, we arent ignorant...we know you like that big cam sound you get when your champions insulator falls out and starts to miss. Not fooling no one.lol
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you hush up! lol
 
Looked at my friends '93 ram 250 forestry service truck today. Has all the underhood stickers still, NV4500, 241 T-Case, 4.10 gears and front and rear limited slip differentials, magnum 360, all wrapped up in beautiful fluorescent snot green. Tune up spec label said Champion RN12YC's, .032 plug gap. Same thing my tune up label says... Why mess with perfection?
 
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