I got an extra 10g/sec by just upgrading the TIP in the LCR for a cutom 3 inch tip all the way to the turbo collar which is 2 inch. That gain was over a samco uprated Tip. 8g/sec more when upgrading Jetex cone also.
Some seem to think that its a pointless excercise since your airflow is restricted by the smallest csa of pipework in the run ie the 2 inch turbo outlet.
The gains actually come from increasing the csa of the bends in the TIP to 3 inch. People who work in the ventillation business will tell you that the tighter the bends the greater the airflow losses.
People who go BT experience big gains, largley due to the superior turbo fitted but also the large TIP and better flowing manifold play a big part also.
Our smaller turbos thrieve on more air, i noticed my duty cycle reduced noticeably reduced.
Custom 3inch TIP and huge Jetex allowed me to run 1.4 bar at red line @ an actuator pressure of 10psi as opposed to 14 psi which was required to get the same boost levels whith my samco Tip and green panel filter.