Wow...good thread.
My experience has shown me on regular Mercruiser motors...the MR43T and the MR43LTS are the Gold Standard.
Stainless steel plated, and they last forever.
Fresh water guys might not care about the stainless, but us saltwater guys need it. I see guys using auto plugs in marine engines quite frequently, but over time, it becomes hard to get those suckers out after a coating of corrosion has formed. And I wonder if that corrosion has an effect on grounding ability.
On another note, I bought some platinum plugs for my Explorer. After a week, the car started running like crap. And I drove it like that for quite a while until I checked the plugs one day and broke one. I went to Carquest to get a replacement and ended up buying a whole new set of double platinum as they didn't have the regular ones. The crappiness disappeared and hasn't come back.
A similar situation occurred to my partner. We replaced the plugs in his Aerostar with platinum, and not only did it run like crap, but it ran worse than before we changed the plugs. The misfires come and go. I'm trying to talk him into the double platinum seeing how it cured my car...but as of yet...he's unconvinced.
I think spark plugs do make a difference, and that there are differences in plug materials that are better for some engines.
But in the end, I think the MR's work just fine with the Merc Thunderbolt ignition. And that the Thunderbolt ignition is just fine for most all performance engines.
GeneD
007
Formerly of Melbourne, Florida
Permanent Resident of St. Petersburg, Florida
1966 Classic 18-2+3