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Dramatic_Hammer
Two pumps stacked on one output drive from the exhaust cam, first stage scavenges the rear of the head, second stage scavenges the front of the head.
Under low load conditions the second stage is going to be returning very little to nothing- under heavy braking and/or turning left it’s going to be working hard. The second stage is absent on the standard (single stage) design, and you are on your own with the oil pooling issue.