| The weight may help a little, but that's really not what they're for. Our stock accessory pulleys are small and heavy, and aftermarket underdrive pulleys are lighter and bigger. A bigger pulley takes a longer amount of time to make one rotation than a smaller pulley. That's where underdriving comes from. So efectively, you're reducing the peak power of these accessories.
Cam gear allows you to alter cam timing if you mill/deck the cylinder head or run nitrous. It makes sure the engine will still keep good timing. This should be tuned on a dyno. | 
