I went to the Unorthodox website and they have released a new pulley that is the stock diameter it is just lighter. It uses the same belts as stock. How much of a power gain would the difference be between the Underdive pulley and Lighten Stock Diameter Pulley?

 

The UDP would be better since it is lighter (by lije .5lbs) and it underdrives. The stock diameter one is for those who are SCed or maybe those who run a huge audio system on the stock alternator.