* The Vehicle Identification Number (VIN): The VIN contains coded information about the vehicle's specifications, including the engine. You can usually find the VIN on the driver's side dashboard, visible through the windshield. Once you have the VIN, you can use a VIN decoder (many are available online) to determine the engine size.
* The Engine Block: The engine itself will have a number cast into the block. This number can be used to identify the specific engine. However, this requires accessing the engine bay, which might be challenging for someone unfamiliar with car maintenance. You'd need to look for a relatively flat surface on the block.
* The Owner's Manual (if available): If you have the original owner's manual for the car, it will specify the engine size.
* The Vehicle's Title or Registration: This sometimes lists the engine displacement, though it's not always reliable.
The most reliable method is using the VIN and a decoder. The engine size for a 1978 Grand Marquis was typically either a 400 cubic inch (6.6L) V8 or a 351 cubic inch (5.7L) V8, but the VIN will definitively tell you which one is in the specific car.
