Yes. The underdog is a full half pound lighter. Weight and where the weight is has an impact on the gains. 1.2 pounds spinning at 4,000 rpm is gonna rob more HP than 1.7 pounds spinning at 4,000 rpms. The rpms magnify the weight. Both will improve HP, Torque and MPG, it's just a matter of how much. If you already have a DZK I wouldn't pull it off and put on an underdog pulley.