Surge holes like this?
The port shrouding on the Pro S housing is more typical on a turbo of this size. By the time the air has reached the rear of the surge slots there is some pressure there. And the other end of the holes are on the suction side of the turbo. Long physics lesson short, high pressure always wants to go to a lower pressure section. Pressure difference = flow. So therefore there will always be flow lost that would normally go into the engine that is now being recycled back through the blades
This is how I understand it anyway, what I know about physics makes me think I'm right and Stao from hypergear originally told me it would be the anti surge slots that are the issue. On a T04Z there is a benifit as such a large air flow might result in some surging. But a small GT30 series doesn't flow enough for me to think anti surge slots necessary.
This is what ive done
But as there is no actual seal in the snout of the Turbo to the housing, there is more then likely a leak between the two, again this will mean a slight loss in flow
This is how I See it anyway, hypergear will make me a new housing but want the whole turbo. Seen as it is my daily, I need the car so this isn't really possible right now