Hola
The TNT or whatever marketing name that you may be thinking of exhaust
manifolds do help with power. They are a bolt on replacement for any of the
Imperials from 1967 to the end of time. One must also remember the exhaust
tubing
must match the manifold. A set of these will help with you freeway cruz when
you set your auto-pilot and the gas gage will have a slower drop.