Bell company is working on new IR missile protection solutions. The news to quote from http://www.vtol.org/pdf/61OperationsII.pdf First picture about original AH-1W exhaust exhale effect to tail. Those pictures have taken at hover mod, 60KIAS, 120KIAS speed about IR trace.
New design AH-Z exhaust system to make less IR trace on tail. The system provieds to make hot exhaust exhale cooling by rotors.
New AH-1Z system effect on IR trace.
The same system on Apache.