I just got a 77 Blazer from my in-laws. I know it is supposed to use leaded gas, but I don’t know what additives I should mix with the unleaded gas that I’ll be putting in it. Thanks for your help.
What leads you to believe it should use leaded gas,leaded gas is bad for catalytic converters.
As I recall that era (1977) issue with unleaded fuel was limited to the valve seats. I would expect that they have been replaced by now and there should be no problem for leaded fuel.
Check at your local auto parts store, they may have a additive to provide protection if the seats have not been replaced. They can tell you if they have it, but check to be sure you need it first. Someone here likely will have more authoritative advice than I have.
My father inlaw told me that it needed leaded gas, so I was just going with what he told me.