I was figured it by exh. gas flow at turbine. During shifting (closed TB) is pressure at turbine much lower (low volume of exh. gase), than kompresor load is lower, as it is spinning mainly by inertia. If surge (opposite airflow) is created at this situation, it try to brake compressor down, but in this situation its spinnig almost free, without power from turbine, so there should be less mechanicall stress to compressor at surge situation.
But opposite situation is during full engine load (acceleraction) when same surge state is created, but compressor have lot of spinning power from turbine, then opposite airflow is come with hard mechanicall stress on it.
Sorry for very simplified description, is mainly becouse of my english, but I hope that is clear what Im try to tell.
I would like to know if my conclusion is correct or not, so please post your comments.
Thank you
Radovan
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