This is from Hahn's site:

The Super 20G-N was designed to accommodate drag racing applications where high RPM and nitrous oxide are utilized. The TDO6H-10CM2 turbine section enables very low exhaust backpressure, which improves HP produced per PSI of boost while reducing thermal stress on high boost engines. The additional airflow and low backpressure characteristics are an ideal match for the addition of nitrous oxide.