The plastic outlet of the original turbo is a restiction on airflow. This considerably reduces the turbo's ability to charge early, which limits low-end torque and performance.
The removal of the plastic outlet is also essential for plug-and-play installation of the st3 turbo, as it alters the orientation of the turbo outlet so that it falls exactly in front of the intake pipe (otherwise disalignment occurs, impossible to correct without modification of the inlet pipe).
