Like you I started with AN-4 and now I'm at AN-8. Seems to let the oil flow out much better, but a sump resevoir would help even more. I just can't figure out where to put one without it being too low. I'm doing a 25 psi check valve on the feed side and may go to 0.010 restrictors.
Edited: Just to be clear it's AN-8 on the return side. Still AN-4 on supply side.
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