Will a 1994 Buick Century 3.1 engine replace 1993 3.3 engine?

No, a 1994 Buick Century 3.1L engine will not be a direct replacement for a 1993 Buick Century 3.3L engine. While they're both Buick V6s, the significant difference in displacement (and likely other internal components) means they won't be interchangeable without extensive modifications, likely making it impractical. The engine mounts, wiring harnesses, and even the bellhousing for the transmission might be incompatible.