Velocity is transformed across the turbine blade as in a wing that produces lift to px. Velocity is increased in the turbo scoll (divergent duct) from the exhaust. Px in the exhaust pipe from valve to the scoll is not relevant as it velocity that is required and not px.
A compound charger is the same transform's across the blade but instead of driving a compressor it drive a shaft onto the crankshaft.
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