5/8” drive spark plugs on LA heads

6pak

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Are there any issues with using the magnum type 5/8” drive spark plugs on the older LA heads that had 13/16” drive plugs?
Dia, reach, and gasket all look the same to me.
 

mderoy340

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Is that a hot plug or cold? Say like a champion n9y or n12y?
5 heat range for NGK. I'm 10:1 340 and run pump gas 93 with RHS iron X heads. 3924 is autolites 4 heat range. Both run clean in my motor. My used plugs from my 67 go in my 73 340 j head street car. The 5/8 plug gives a little more socket room with headers.
I won't run champion in my lawnmower. Years ago a set I bought had 3 bad plugs.
 

QuickDart360

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5 heat range for NGK. I'm 10:1 340 and run pump gas 93 with RHS iron X heads. 3924 is autolites 4 heat range. Both run clean in my motor. My used plugs from my 67 go in my 73 340 j head street car. The 5/8 plug gives a little more socket room with headers.
I won't run champion in my lawnmower. Years ago a set I bought had 3 bad plugs.
Wasn't promoting champions just wanted to get an idea of the heat range as compared to champion. Since I am more familiar with these.
 

Kendog 170

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Funny, I never had an issue with Champion but have had 2 failed New plugs with Autolite :eek: I am not promoting Champion either .
 

mderoy340

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Agree with both of you about plug brands. The ngk/autolites have worked well for me with my old reliable msd 6al analog box.
 

Mark2205

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I've used Autolite 3923 on my 340 for quite some time.
 

Dan the man

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Before getting my 360 I really wanted a 340. Found one at a a car show swap meet. Sadly they seller wanted 1000 bucks for a bare block! This was about 1994!! Way out of my budget then.
Before getting my 360 I really wanted a 340. Found one at a a car show swap meet. Sadly they seller wanted 1000 bucks for a bare block! This was about 1994!! Way out of my budget then.
That's way to much.
 

Scody21

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Are there any issues with using the magnum type 5/8” drive spark plugs on the older LA heads that had 13/16” drive plugs?
Dia, reach, and gasket all look the same to me.

Nope. I use NKG - BKR6E / #6962 in my 340’s with J heads and eddy heads, stock 318 and 5.9 in my 02 ram.
 

6pak

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OP Here.
Great.
It looked good to me, but I may have overlooked something.
This turned into a brand and heat range thread.
- brings me to……,
Thinkin,…
Iron heads should usually run colder plugs with increased compression.
Aluminum, .. not so much.
Exotic metal plugs are good for longevity. And old copper cores are better for making fire.

but, does anyone have an opinion on the E3s?
 

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