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Old 06-05-2008, 12:20 PM
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Spark Plugs which ones big block chevy

How do i tell which one i will need , i look online and it shows it can take either Large or small hex spark plugs used, crate motor usage . 3964291....69-72...rect..CLOSED..396, 402, 427, 454, 109cc chamber .
I try long 3/4 reach ( acr43xls ) and when i remove the plug i can see where out of all those threads it only uses about 4/5 of the threads . Oh mine are also dated jan 71 .
What plugs can i goto store and see if they fit ?

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Old 06-05-2008, 12:51 PM
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AC Delco R43TS should work just fine. (I think that is the number I am having trouble remembering off hand)
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Old 06-05-2008, 01:46 PM
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I run a br8es NGK in my closed chamber heads you will be looking for either a flat seat or tapered seat plug. My heads have a flat seat which uses a washer and is 13/16 hex the tapered seats dont use a washer and are usually 5/8 hex
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Old 06-05-2008, 08:04 PM
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69 castings use the old "N" series plugs 13/16 hex, partially threaded 3/4 reach. 70-72 use the taper seat 5/8 hex plugs.

Back in the day I bought a brand new 70 BB in late 69. NOBODY had the correct plugs available for the car. Till early spring of 70.
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Old 06-06-2008, 04:40 AM
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My heads are a 69 casting
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Old 06-06-2008, 06:36 AM
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My heads are the 70 425HP 454 heads. Which is why I said the Delco's would work. They are the 5/8's taper
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Old 06-06-2008, 08:10 AM
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Thanks to those who replied , The hole is hard to see but it looks like theres a hole ( larger then spark plug thread ) not threaded then further down a threaded hole , just hard to see if its flat or not . I guess its either a .460 reach or a .750 , The parts store says it could be a .708 reach . This is where iam lost . But if i buy say one 3/4 reach and one such as the r45ts ( guessing that a 5/8 th 460 length ? ) to see which it will accept . I wouldn't think the .460 reach would even start in one needing a .750 reach plug .


Adding this part = the ts plug won't even begin to thread , so it must be the 3/4 length , i just need to find the heat range i need .

Last edited by Tommy B; 06-06-2008 at 09:37 AM.
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Old 07-17-2010, 08:23 PM
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What spark will fit my big block?

I just had my big block chev on the dyno and it ran terrible. When I got home I pulled the plugs and I noticed they were only screwed in a couple of threads and they should go in 9 or 10. It looks like the 13/16 hex is hitting the edge of the first counter bore on the plug hole. I have never had this problem before. I tried to screw in a peanut plug and it wont go either. I think that is because the motor was ran with the other plugs partially installed. This motor I know takes the .750 long plugs. The heads are closed chamber rec port 65 427 corvette iron heads. T same plug that wont fit my iron heads screw right in my aluminum L88 head. Whats going on am I missing something?
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Old 07-17-2010, 08:25 PM
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Quote:
Originally Posted by RS SS L88
I just had my big block chev on the dyno and it ran terrible. When I got home I pulled the plugs and I noticed they were only screwed in a couple of threads and they should go in 9 or 10. It looks like the 13/16 hex is hitting the edge of the first counter bore on the plug hole. I have never had this problem before. I tried to screw in a peanut plug and it wont go either. I think that is because the motor was ran with the other plugs partially installed. This motor I know takes the .750 long plugs. The heads are closed chamber rec port 65 427 corvette iron heads. T same plug that wont fit my iron heads screw right in my aluminum L88 head. Whats going on am I missing something?
start a new thread, you'll get more answers. This one's 2 years old already.
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