In that case, the only time much filtering is going on is at idle, or other times when the oil distributor is at least partially closed. Once the pressures are close to equal on both sides of the distribution valve, little if any flow will get through the filter. I wonder if that's another way to assure the rods and mains get enough oil flow to stay lubed? Full pressure engines do drain the filter back to the oil pan through a port to the pan rail and a notch in the pan gasket.
Jerry

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