cool, since I get to be first here, (unless someone posts while I type, DOH!) then I say, imagine blowing through a pipe of 1" diametre, with a very rough inner texture inside it, imagine the reduced effective diametre, due to the turbulence created by the roughness. Now blowing through a 1" smooth tube, it feels more open, easier to flow through.
It isn't a 400% increase in power mod, but it will give the gains you can imagine. Air (and fuel with it) will flow to the cylinders much (relatively speaking) better than before.