Will a 455 engine fit in 1986 buick regal?

A 455 cubic inch Oldsmobile engine is significantly larger than the engines that came stock in a 1986 Buick Regal. Fitting it would require extensive modifications, and is unlikely to be a straightforward bolt-in swap. You'd need to address:

* Engine Bay Clearance: The 455 is much bigger and taller. Significant modifications to the firewall, inner fenders, and possibly even the frame rails might be necessary.

* Transmission and Drivetrain: The transmission and associated components (driveshaft, axles, etc.) would likely need to be replaced to accommodate the 455.

* Mounting: New engine mounts would absolutely be required.

* Exhaust System: A custom exhaust system would be necessary.

* Wiring Harness: The wiring harness would likely need modification or replacement.

* Cooling System: A more robust cooling system would likely be needed to handle the larger engine's heat output.

In short, while *technically* possible with significant fabrication and custom work, it's a very substantial project far beyond a simple engine swap. It would require considerable mechanical expertise and resources. It's not a project for beginners.