I see people modifying their 4th generation accords to gain more power. One of the most common and effective bolt-on ways to increase power is replacing the intake manifold, plenum, and throttle body. Specifically, they change their stock F22A1 configuration with the manifold/plenum/throttle body with an H23. Supposedly this manifold allows for greater airflow, and the throttle body is of a larger diameter anyways, furthering the benefit.
People are always lauding their new setups, how this provides +10HP and really makes a difference in "the high end."
I don't drive in "the high end,"; my rpms are generally almost always below 3000!
My interest isn't so much in power (though every once in a while it's nice to have fun with it) as much as enhancing reliability and fuel economy. Would these enhancements do anything to improve fuel economy? I would think that the the less-restrictive design of these new components would reduce the effort necessary to breathe, requiring less fuel to be burned to maintain a given speed. Of course if this is true, it could be negated by a driver anxious to realize performance gains . But just suppose said driver had good self control, would any benefit in fuel economy be realized?