The filter outlet restriction doesn't change the dP across the filter. ... I disagree, in a model it could with a capacious, low efficiency (low R value) inserted into a small engine model; but as I mentioned later in the discussion likely not in practice. Must use care when discussing a bench model and using the term never.
There is no way that the outlet pressure can be higher than the inlet pressure. If it was, the oil would be flowing backwards through the filter. ... . I never stated that, did I? I think I wrote outlet restriction
Again, there is no way the fluid pressure on the outlet of the filter is higher than the pressure on the inlet. The pressure on the inlet has to be higher than the outlet in order to make fluid flow from the inlet to the outlet. Basic fluid dynamics. Again, I never stated that, did I intimate that in some way?
There is not way an oil filter is more flow restrictive than an engine's oiling system. I find that most oil filters are only about 1/15th the flow restiction of an engine oiling system. I think you meant less. If you had a filter canister with no element - just the centre tube - would not there be NO delta p? Do you have examples? How was this data obtained?
Hard to say exactly what the Subaru service manual oil pump spec really means. I've addressed this before when that spec sheet has popped up in previous discussions. Yes, the "discharge pressure" seems low for oil at 80C, but maybe those oiling systems are relatively low flow restriction. Says at 5000 RPM that the pump discharge is 49.7 qt/min (12.4 GPM). That's not out of the question, but yes I agree is that actually the flow rate seen in the engine with the pump pressure relief set to 85 PSI as shown in the specs? If the engine does flow that much oil volume, then that's one reason why Subaru shows the OEM filter to have a high 23.2 PSI bypass valve setting.
Yes, this does beg for more information from subaru.
Thanks for the continued discussion. Just thinking and learning here.