As the oil,from the oil pan,moves toward the pump,it eventually moves upward through a passage on it's way to the suction side of the pump cavity. If you could swim upward through this passage and it were clear,you would eventually notice that the pump gears were directly in front of you but that the passage doesn't take a turn toward the gears there. It continues upward to a point above the gears,makes a 90 degree turn and another and immediate 90 degree turn and travels down another passage parallel to the one you just swam up and enters the suction side of the pump. The one and only thing that the hole does is eliminate the last 180 degree turn and that seems like a good thing. The hole is drilled through the wall separating the parallel up and down passages at the point coming up the passage where you would notice the gears right in front of you. In stead of the fluid continuing upward and negotiating that final 180 turn,a lot of it is pushed through the hole in the wall by atmospheric pressure in response to the vacuum created on that side of the pump. It's a shortcut that eliminates a turn and that seems good. It's the one and only thing that it does and Earl doesn't even mention it.
The booster plate does one and only one other,different,and distinct thing. It creates a continuous/uninterrupted flat surface,with no holes or cavities,for the bottoms of the gears to ride up against. This is the one and only objective of the plate. It causes the gears to move fluid more efficiently.
As the gears move fluid toward the engine it is allowed to move into another passage that is round and has a piston (pressure regulator valve) at the end of it with a spring behind it. The pressure builds to a point where it moves the piston against the spring pressure and eventually moves the piston enough that some fluid can leak past the piston. This is how the pressure is regulated. This fluid has to be allowed to go somewhere or else the pressure would continue to build. The factory sent this fluid back to the bottom of the gears to re enter the pump and be moved along again. With the plate installed the fluid is no longer allowed to re enter the pump there. The modification that is required to be done to the cover is done to re route this oil back to the upward moving passage where we see the gears in front of us a little bit before and below the hole that Earl drills. The positive effect of the booster plate is not caused by re routing this oil. Rather the oil has to be re routed because of the actual purpose of the plate which is to create efficiency with the uninterrupted flat surface of the plate.
The hole and the plate are two very different and distinctive things. Neither one of these things does what the other does. There's nothing that you can do to the plate that accomplishes what the hole does and their is no hole that you can drill anywhere that accomplishes what the plate does.
