I thought higher compression generally meant hotter combustion temps? I wouldn't be worried about that compression level anyway. My build ended up about 9.3:1, and I'm running auto lite copper 25's. I was always told the platinum plugs were a waste of Mamet, so I never ran them and have had good luck with copper. Did you rebuild your EEC-V motor?
This is the short block from the donor truck, a 1990 F-250. We rebuilt that at .030 over, using the 1988-1992 pistons, a Sig Erson cam and everything balanced. The heads are a pair of F3TZs with Scorpion rockers.
The engine in the truck is the original 1986 short block with the top end of the 1990 engine. It is only maybe 8.0:1 compression as a result. The reason for asking, the VECI label for the EEC-V California models call for ASF-42P plugs, I am currently running ASF-42C plugs as that is what the 1990 spec is.
I have my new engine getting ready for installation. The normal plug for the EFI 460 is ASF-42P. I have raised the compression to 9.23:1, the question is, should I drop back one heat range to ASF-32P?
IMHO, no....because there is not just the CR but the cylinder psi as well that factors into this......and the CR hasn't been raised that much really 9just enough to make it nice). This is fine for the initial start-up and break-in period since you're going to be driving it gently......
because of the unleaded gas, plug color is not going to be a good short term indicator.....once it's broken in, then I would try some gentle lugging to check for pinging.....if there's none, I would just periodically check the plugs and go have fun!