Foeraus is right, to a point.
Anytime you modify the engine, ostensibly you do so to increase the amount of power it produces. The raw force generated by an engine is measured in ft/lbs or n/m, depending on what side of the border you're from (eh?). This is force over distance- Turning power. Modifying your engine will increase the amount of this force, but not in any seriously appreciable amount without F/I or more displacement.
Horsepower is a derivative of torque. HP=(torque*RPM)/5252
So, increase torque by a little, and you increase hp by a greater margin as you rev up. That's how Hondas make 240hp with a puny <2.0L engine- They rev the hell out of it.