An oil control valve for a cam phaser of an internal combustion engine where the spool is positioned by an external actuator. The valve includes a spool assembly including a spool that is axially movable in a central opening, and there is at least one groove in the spool. The groove substantially increases fluid flow through the hydraulic valve when opened. By controlling the size and position of the groove, the amount of the fluid flow may be controlled. Further fluid flow control may be had by controlling the size of holes in the spool. The increase of fluid flow attributable to the groove may be at least 50%, 100% or even 200% compared with the at least one groove being absent.