Spark plugs. Why is it so hard?

NGK developed the copper core spark plug in 1965. Holley did it 7 years later.....
Maybe Holley was the first American company to market them.


If you have a link to this information I’d like to see it. I can find nothing that validates your claim. Doesn’t mean you are wrong. Just means I can’t find anywhere where even NGK says that. And really, who cares who developed it? Things can be developed simultaneously and all the parties involved may have no knowledge of it.