Holley 12-880 Billet Adjustable Regulator Features:

Note: The regulator has a PSI range of 4-15 PSI. It also includes a second spring that can be installed for the 16-65 PSI range. Determine approximate fuel pressure your system will require. If your fuel pressure requirement is between 4 and 15 psi, the factory installed regulator spring is the proper spring. If your fuel pressure requirement is between 16 and 65 psi, insure the pressure adjustment set screw is backed out all the way, remove the 4 cover screws and cover, remove the factory installed spring, replace it with the high pressure spring, and reassemble the regulator.