If a good heat range on a iron head combo was a NGK7, then an aluminum head replaced the iron head with the same cc, same compression, same cam, would the heat range of the plug need to be hotter for the aluminum head?
If so, what would be a new suggested heat range be for the alum head?
Thanks

I would try the same plugs, if they will fit into both heads properly, if not I would use the same heat range, brand and type, protruded or retracted gap in the new heads It is way safer IMO to use to cold of a plug instead of to hot of one

Cab,
My assumption is that since the iron heads holds more heat which caused me to use a colder plug, that the aluminum plug would need to be hotter.

Thanks Cab!

One heat range cooler for iron heads.

I went to the only place I was sure there was the same engine with different material heads, early '90s Chevrolet. I figured I'd debunk your theory.

The Camaro 5.7 has aluminum heads,the Caprice 5.7 has iron heads. To my surprise, they had different plugs for each, the plugs were one step cooler for iron heads, or saying it another way, aluminum heads needed one step hotter plug.

So good deduction, at least on a chevy 5.7.
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R.

Thank you DD!!!! Great info!!