Due to the boost spiking that is common on the VA WRX (that becomes even worse with exhaust upgrades), our Stage2 maps require the deletion of the restrictor pill. If this is not done, underboosting will result. The hose and pill in question are shown below. The entire hose can be replaced with a new section of 6mm or 1/4" silicone vacuum hose (clamp each end securely!) and the factory hose can be set aside. Alternately, you may remove the pill from the OEM hose, set the pill aside and reinstall the hose.
COBB Product Install Instructions for Subaru Vehicles
Main Installation Instruction Repository for Subaru Parts
Calibration Map Notes for Subaru Vehicles
Link to Subaru Map Notes to see what map you should be on given the parts you've added