PLatinums are crap IMHO period. I ran them ONE DAY in my old '85 4-banger. I had about half the power and I lost half my mileage in that one day. Changed back to Champions and instantly had my power & mileage back. It was scary how much of a difference it made. My '87 Notch had CRAPNUMS in there when I bought it. I've been running RV15YC4's in it since and I'm getting 22mpg and pretty damn decent power, too. The biggest thing is that my engine no longer pings up top. Go with the suggested copper plugs and you should be better off. STAY AWAY FROM SPLITFIRES!!!
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Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch 