I'm getting ready to do an MSD ignition upgrade on my Seville. You know they have that, buy all you distributor parts in one kit to upgrade your stock HEI system. I will also be running MSD 8.5 wires

Anyway the question is what plugs does everyone use. There are AC Delco Rapid Fires in there now which I loved but they have well over 100k on them and it's time for some TLC.

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Good question, I would like to know as well my STS is up to 50K miles and the service warrenty is now over, finally I get to work on it my self.

I use the Autolite 764 Coppers. AMAZING plug.

Use copper plugs. They do the job, do it well, and won't break the bank. Don't bother with the $5.99 a plug quad-tip platinums, or whatever they are. They aren't worth it.

Im a Split Fire fan. But I went in to an auto parts store and said they do no sell them anymore! (Sad)

Autolites or Motorcraft for me. They probably don't fit the GM?

Either way stick with simple coppers for best performance or platinums, iridiums or silver for longest life.

Plats do nothing, the FTC sued the crap out of Bosch for making false claims about platinum plugs.