The porting is hidden unterneath the pump handle, in the join / chink between the tubes, in space where is the pump handle not guided, so the contact surface and pump-stroke is not affected. The change is hidden, is not visible from outside.
There is space for 2x 19 holes ID 2mm (see photo) or 2x 14 holes ID 2,5mm (see schematics below).
This way you can reduce the "sound patch" of your PGP. Subjectively the sound reduction is between 10-15% when you already have tunned marker with lightened hammer (I do not think that the porting will do something with the "Ploop" sound caused by the bouncing).
I was suprised, but the CO2 efficiency has been not affected, at least on tunned marker (the chrono results before and after do not lie).
Velocity graph of tunned marker after and before:
Schematics of the porting placement on ZGP-94: