Those motors required the premium of the day, which was 99+ octane(?). I wouldn't ever put less than premium in it. And if you're going to thrash it, maybe add some octane boost.
My YS code 389 runs OK on 93 octane for normal driving but when I punch it, I get knocking at WOT at high RPM's. The one time I put 87 octane in (after I ran out of gas), the engine wouldn't shut off when I got to the gas station (dieseling).
