Ported

The ported vacuum control system utilizes a slow type port in the carburetor throttle body which is exposed to an increasing ratio of manifold vacuum as the throttle blade opens. This throttle bore port is connected through an external nipple directly to the EGR valve. The flow rate is dependent on three variables, 1) manifold vacuum, 2) throttle position, and 3) exhaust gas back pressure. Recycle at wide open throttle is eliminated by calibrating the valve opening point above manifold vacuums available at wide open throttle as port vacuum cannot exceed manifold vacuum. Elimination of wide open throttle recycle provides maximum performance.