Zinc additives contaminate catalytic converters so what oil should be run in say a 1987 Suburban with 350? Been running regular Castrol but maybe add half bottle of zinc additive? o No: It's a Chevy so of course it smokes a bit on startup....so I know some oil is getting to the cat.
I wouldn't worry about zinc in that engine - the cam is long broken in and there isn't much spring pressure. As far as zinc hurting the cat, it has been "zincked" for 15+ years. OBDII can monitor cat efficiency, but that didn't start until 1996.
