A rotary shaft pump for increasing supplied oil pressure to a pressure responsive device in an internal combustion engine. The pump includes a housing adapted to carry a plurality of axially spaced journals of a rotatable shaft. The shaft also includes at least one pumping element having a larger diameter than the other journals of the shaft. A cam phaser carried on one end of the shaft receives pressurized oil from the engine through oil passages extending through the housing and the shaft. As the oil is pumped through the oil passages of the shaft, the oil is centrifugally pumped through a radially extending pumping passage extending though the pumping element to boost oil pressure supplied to the cam phaser.