No, the w9dco or w9dc is recommended or used for my stock model, but I have a 6.0 litre modification. The engine now runs hot. I don't know what the previous plugs were. One of my relatives brought it to someone and they exchanged the spark plugs out with w9dc. Now the plugs are overburned, all of them. I assume the extra gas or cams for combustion or whatever the modification is causing this. I checked the w8dc, but those are for the 420 SEL stock. I also checked with a cross-reference chart to see if the heat range changed any with these w8dc, but it doesn't change at all. I also assumed the same, but I don't think it is. Also, why would the 430 SEL, a less powerful engine than the 560 use a colder plug? Thanks, for the help
Any other suggestions.