the way i understood it is this , when u port and polish a head on a turbo car u get a psi drop and the reason for this is becasue the turbo doesnt have to work as hard to force the air through the head there for its means that the airflow is a lot greater ....hes arally engine builder and uses flow bench as well so i belive him lol ....and as for the cvh u can port it out a lot cos of the crap inlet design