The cast aluminium throttle body inlet pipe has a rather poorly designed
entry port at the point where it mates to the delivery pipe from the intercooler.
The ridge is rough and uneven with its thickness ranging from 3 to 6 mm,
which constitutes a noticeable restriction to the air flow.
Porting the pipe is a well-known and simple modification. The goal is
to smooth the ridge, thin down and polish the walls around the entry port,
providing a better transition from the delivery pipe. You can use a Dremel
or more traditional tools like a round file and sandpaper.