Originally Posted by Mike@GTM

You are missing time in your equation.

Pressure * Volume/time = #moles/time * Gas Constant * Temperature

GT25 = 22lbs/min@8psi at the choke line on the compressor map
GT60 = 125lbs/min@8psi at the choke line on the compressor map

Remember that horsepower is work over time. The more airflow you have (cfm, lbs/min, etc.), the more power you make provided you have enough fuel.

Boost pressure is the measure of restriction to airflow, which is why it is practically meaningless when trying to determine horsepower. Lbs/min and cfm are what matters...again, because you are relating a time based unit to a time based unit (airflow to horsepower).

Back on topic, Phunk nailed it.