Fig. 63.3
Fig. 63.4
Add these Pressure-Balance grooves across the idler and drive-gear cavity ends to provide Hydrostatic Balancing of the gears. This balancing helps stabilize oil flow through the pump and reduces gear chatter which aggravates Spark Scatter. The grooves are approximately 0.03125-inch deep and 0.0625 to 0.125-inch wide. Note the vertical grooves going up the side of the pump body these grooves match up with the grooves in the pump cover. There is a groove in the side of the body for the drive gear also, it just can't be seen at this view angle.
NOTE: The use of a Big-Block pump also helps prevent spark scatter because of the 12 gear teeth as apposed to only 7 in the small-block pump.