The diameter of the Boeing 747-400 engines is approximately 2 meters, with various manufacturers like Pratt & Whitney, General Electric, and Rolls Royce producing engines with fan diameters around this size. The Pratt & Whitney PW4000 series has a fan tip diameter of about 2.39 meters, while the Airbus A380's GP7000 engines feature a fan diameter of 2.95 meters (116 inches). Engine thrust for the 747-400 models reaches up to 70,000 lbs per engine, while the GP7000 is rated at 81,500 lbs. The discussion highlights the significant variations in engine sizes and thrust capabilities among different manufacturers and aircraft models.