I have a 1978 Fairmont GXL XC 4.1 with Extractors, bottom stock end, an Alloy head (XD or XE not sure) ported and polished and port matched to triple 45 DCOE Sidedraft Webers, I was running NGK BP6E S Plugs (I think these were for the cast iron head and probably didn't seat properly and ran black, along with backfiring), I have just put a set of NGK BP5FS plugs in (supposedly correct), improved already, but seems confusion on what is recommended, any assistance appreciated.
Only used for street driving.
Only used for street driving.