AFR misleading? Plugs tell a better story?

Unless you have 8:1 compression that plug may be too hot.[/QUOTE]

I’m going to venture a guess here but 72 340 with iron heads and a whiplash cam tells me 8:1 might be close. That’s what those cams are for. Low compression and “that muscle car idle”. Op were the heads shaved at all or do you know the chamber volume? Maybe some compression test readings?