CHARLOTTE, N.C. — NASCAR’s Next Gen car technology has leveled up and cooled down. The stock car racing sanctioning body has teamed up with digital manufacturing company Stratasys to 3D print production parts for all of its Next Gen racecars. The parts include a windshield air duct piece and underside NACA duct that are used for cooling driver cockpits. They are the first 3D printed production parts to be used on every Next Gen car. Although Stratasys was officially announced as a NASCAR Competition Partner on Tuesday, its parts have been used on the Next Gen cars for months. During a test ses…