[SmokinDiesel]

are you talking about the turbo surgeing or barking?, i always thought they were two different things.

They are indeed two different things. "Barking" a turbo is from cutting the fuel supply off instantly, and air is still trying to move. Since the fuel supply is cut off, that air HAS to find a place to escape, and the easiest place for the air to go, is back through the charger.

"Surgeing" is more or less starving the charger. At certain rpm's and fuel, the charger will almost start "huffing"

Two TOTALLY different things

 

[SmokinDiesel]

OK, you made me go look, because I thought one (barking) was a symptom of the other (surge)

According to Garrett.
Surge is the left hand boundary of the compressor map. Operation to the left of this line represents a region of flow instability. This region is characterized by mild flutter to wildly fluctuating boost and “barking” from the compressor. Continued operation within this region can lead to premature turbo failure due to heavy thrust loading.
Surge is most commonly experienced when one of two situations exist. The first and most damaging is surge under load. It can be an indication that your compressor is too large. Surge is also commonly experienced when the throttle is quickly closed after boosting. This occurs because mass flow is drastically reduced as the throttle is closed, but the turbo is still spinning and generating boost. This immediately drives the operating point to the far left of the compressor map, right into surge.



Surge will decay once the turbo speed finally slows enough to reduce the boost and move the operating point back into the stable region. This situation is commonly addressed by using a Blow-Off Valves (BOV) or bypass valve. A BOV functions to vent intake pressure to atmosphere so that the mass flow ramps down smoothly, keeping the compressor out of surge. In the case of a recirculating bypass valve, the airflow is recirculated back to the compressor inlet.

Yup ... Exactly what I said, just with a little different take of things. Some people will refer to a "bark" as a "surge" .. and a "surge" as a "bark". But in retrospect, they are two different animals.