o No: On NGK plugs is the higher the number the colder the plug? Which would be a good starting point for plugs on a iron headed 9.8 to1 comp stage1? We have a fleet-farm near us with NGK plugs. Can I go by the NGK book for a 455 or will that be to hot? Tom
the UR5 is the standard-use plug, and other guys here have used them. You could try the UR6 if the y have them(yes, 6 is colder than 5) but in your engine I think 5's would be fine.
