Spark Plugs
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Spark Plugs

  1. #1
    Senior Member Flat Fan's Avatar
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    Default Spark Plugs

    I'm running a 468 with an 8-71 2 750 holley dp, solid roller and a pair of 345 AFR's. On the current set up it has 8-9 pounds of boost on 91 oct. The spark plugs I'm using is Autolite AR3931, and I think there a bit hot. When I look at the ground strap its like a brown color all the way to the base. What number should I change to that stays a standard type plug. Thanks in advance.

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    Senior Member hot-rod 21's Avatar
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    With my blown set up on pump gas I was running AR3934 never an issue.

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    Senior Member jockorace's Avatar
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    I'm also running the AR 3934 plugs in a nearly identical motor. Running a magneto in mine. Jocko

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    Senior Member Flat Fan's Avatar
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    I haven't had any problems yet, and made plenty of hard passes on the engine. The reason I ask is the AFR tech said to 1-2 steps lower for a blower motor than what the manual has on it which is AR3932. Should I keep running this plug. Do you have a picture of what a typical plug coloring is.
    Thanks again

  7. #5
    Frank my lord Blown$um's Avatar
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    Default the color of plugs

    i used to have trouble correctly reading plugs then realized autolite and several other manufactures have some type of black coating on them so they dont rust i would think anyways. but being black in color makes it hard to really see heat changes , and different fuels leave different deposits on the plugs . for example sonoco 116 has heavy amounts of lead in it and leaves a grayish in color deposit on plugs which makes it hard to correctly read plugs . but what i have found is that ngk makes all the same plugs and their silver in color which shows any discoloration in the tang and one of the most important parts is how far the heat is traveling up the thread count which is unmistakable when you see it , you wont be disappointed you might want to try a set. . just my two cents if it may help anybody on here.
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    i'm back!! 1QuickCP's Avatar
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    NGK try heat range "9" for starters....easy to read

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    Liquid Louie flatcrzy's Avatar
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    I've got the same issue, running a 496" blown BBC 966hp and my plugs are Autolite 26 copper core plugs, hard to find and wanted to change to NGK but cannot cross reference these two!

  10. #8
    Frank my lord Blown$um's Avatar
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    Default plugs crossed

    autolite 26 crossed over in my book to ngk stock #2451 / part # ur45 , book is about 3 years old and ngk likes to change their part numbers every 3 years it seems. you can call napa and they can give current numbers if you give them the numbers i gave you. but for all i know my numbers are still current .
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  11. #9
    gn7
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    Quote Originally Posted by flatcrzy View Post
    I've got the same issue, running a 496" blown BBC 966hp and my plugs are Autolite 26 copper core plugs, hard to find and wanted to change to NGK but cannot cross reference these two!
    Autolite 26 is a .460 reeach, tapered seat, PROJECTED TIP plug. Can't say I recommend anybody runs a projected tip plug in a blower deal.

    Your NGK number is a 3442



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  12. #10
    Senior Member jockorace's Avatar
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    Quote Originally Posted by Blown$um View Post
    i used to have trouble correctly reading plugs then realized autolite and several other manufactures have some type of black coating on them so they dont rust i would think anyways. but being black in color makes it hard to really see heat changes , and different fuels leave different deposits on the plugs . for example sonoco 116 has heavy amounts of lead in it and leaves a grayish in color deposit on plugs which makes it hard to correctly read plugs . but what i have found is that ngk makes all the same plugs and their silver in color which shows any discoloration in the tang and one of the most important parts is how far the heat is traveling up the thread count which is unmistakable when you see it , you wont be disappointed you might want to try a set. . just my two cents if it may help anybody on here.
    You must be referring to just the standard Autolite plugs with the black color. As you can see, these AR series plugs are not black and more importantly have the cut back tips. It sure saves a lot of hassle cutting the tips back by hacksaw or cut-off wheel! Jocko
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  13. #11
    Liquid Louie flatcrzy's Avatar
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    Quote Originally Posted by gn7 View Post
    Autolite 26 is a .460 reeach, tapered seat, PROJECTED TIP plug. Can't say I recommend anybody runs a projected tip plug in a blower deal.
    Your NGK number is a 3442
    Thanks, that's what it had in it and after getting her re jetted I wanted to through new plugs in it! I'll put a set of the NGKs in and give it a color check and have Fatheads guy check it out!

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