what are the major differences between the 2 clutches. i have both clutches side by side and they look the same. also, i notice the 250 pressure plate has lightening holes where the 500 those hole are not cut out...if shaving a few grams off the flywheel helps the motor rev easier, how would shaving a few grams off the clutch set up help?

So basically,,,,

9 grams off the clutch assembly would be roughly equal to only 3 grams off the flywheel. In effect,,,

Correct?

So instead of shaving the outside of the flywheel, it would (in theory) best to take the material from the center point out to a few mm short of the edge. Or drill holes around it front the center out. But you can't really do that without compromising the integrity of the flywheel right? That's why most lightened flywheels are just skimmed across the face .0xx" and the outer side/ring is left alone?

"A flywheel will be the most effective flywheel if all of the mass is concentrated at the farthest distance possible from the axis of rotation."

This is what made me think that you meant that the center/face of the flywheel needed to be shaved,,,

But alas, this is a clutch thread, not a 'flywheel lightening theory' thread and I don't wanna thread jack,,,,, I do enjoy learning though! Is there already a flywheel thread or what?