360 LA installing Promaxx Aluminum heads

qkcuda said

The engine is a 361 with an actual calculated 8.5:1 compression ratio. I upgraded to a small cam which is essentially the same as the stock 383 four barrel cam. I figured due to the low compression I would stick with a hotter plug, hence the 14's. I am not up on the whole ground strap and thread reading. I could drop down to a 12 if that seems better.

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Yeah, you have a problem with heat range availability with that style of plug. That J series short reach plug SUCKS for heat range. Everyone pretty much has made obsolete that style of plug.

You might want to screw a set of 12’s in there and see what they look like. Then you may want to see what Autolite and NGK have in that heat range because even though the cross reference charts show the equivalent heat range, they can and often are different.

The only way to know for sure is to start testing with other brands of plugs to see if you can get the heat range where the plug wants it.