Does anyone have any suggestions on what is the best spark plug to use in a 401 nailhead? It has the pertronix HEI, two 600 carters, NH600 poston cam. It has the high heat range a/c delco's in it now, but seems to run a little on the warmer side. Could the high heat plugs be keeping the heat in the cylinder and making it run warm? I do have the timing advanced a ways, but it never pings. I think it's about 30 degrees total advance and I run 92 octane with octane boost and lead substitute. The weird thing is it will idle all day long at 180 degrees, just gets hot on the highway. Maybe I wil try changing the distributor advance springs to heavier ones.

Any suggestions will be helpfull

Thank's 66 buick guy