It depends on the spring used. My testing had a 15 PSI spring range from 12 PSI at idle to 15 PSI at high RPM's. My testing had a 22 PSI spring at 18 PSI at idle and 22 PSI at high RPM. My testing had a 30 PSI spring at 25 PSI at idle and 30 PSI at high RPM's.

dave w