* New motor mounts: The V6 and V8 have completely different mounting points.
* Modified or custom headers and exhaust: The V8 will be significantly wider and longer.
* Potential transmission issues: You'll need a transmission compatible with the V8, and that might require modifications to the transmission tunnel or driveshaft.
* Wiring harness modifications: The V6 and V8 have different wiring harnesses.
* Cooling system upgrades: The V8 will generate more heat and may require a larger radiator or other cooling system modifications.
While *possible* with a lot of custom fabrication, it's a very involved and expensive project, not a simple swap.
The biggest engine that would fit reasonably *without* major fabrication would likely be a larger V6. Even then, some minor modifications might be needed. You'd have to research specific V6 options and their dimensions to ensure compatibility. Finding a suitable, higher-performance V6 from another GM car of the same era (or slightly later) is the more practical route to increasing engine power in your 1986 Cutlass Supreme.
