Only way to increase your "horsepower" is heavier limbs, a more efficient cam/limbs (not really feasible at this point), or a longer draw stroke. Energy comes from the limbs. Arrow is just a vessel.Only way to increase my horsepower is go up in draw weight and/or heavier arrows.
Theoretically, the ideal arrow weight if we're talking about delivering the maximum amount of energy that the bow creates would lie at the highest point of a bell curve. Not too heavy, not too light. Just enough mass to absorb as much energy as possible, and no more.
Easton, who has published a lot of info on all things archery over the years, recommends 35ft/lbs of energy for ethically harvesting whitetails. Most guys setups generate and deliver more than that.