Kai is right. w/ the less rotating mass, the engine will rev quicker, but it will also fall much faster due to lack of inertia. I have replaced just my crank pulley w/ a lightweight unorthodox unit, and will be replacing the clutch & flywheel this weekend (clutchmasters aluminum flywheel). Just getting rid of the parasitic drag attached directly to the crank is what I have heard you want to do. I can't really tell a difference w/ just the new crank pulley on there, but when I pulled the factory one off, that think weighed a TON compared to the UR.