Engines number locations vary, but most are fairly easy to find on a stamped plate on top of the engine. This plate typically lists both the vehicle identification number and the engine number.
Vehicle identification numbers varied in length before 1981, but cars made since then have 17-digit numbers, as of 2015. The engine number is shorter and, like the VIN, it reveals information about the engine itself. A vehicle's VIN is generally placed in other areas of the vehicle as well, since it's possible to replace a car's engine. The inside of the driver's door, for example, is a popular location for VINs. In addition, car registration forms typically list the VIN, but not the engine number.