If I Recall Correctly, their are several bypass filter reps that recommend a full zero pressure drop on their filtering configuration. I'm not one to say that it won't work as well with the return to the sandwich with a 2 pounds/square inch differential, because I don't have one set up like that. Amsoil sells a sandwich adapter that is entirely open, save the 4 cross members of the sandwich structure, that they use for oil for one of their applications. It provides complete flow down to the full flow filter, and at the same time, as oil is backed up there waiting for the engine to take it (via the full flow media) a certain portion is redirected to a bypass filter by one of the ports. From their bypass, that has a restrictor built in, it then is directed to the zero drop configuration. I've seen this on OilGuard, Franz Filters, and Gulf Coast filters as well. The key to any good retention in filtering is to slow down the flow to an acceptable rate. Meaning, you don't want 95PSI on that filter pushing through with the restrictor out. It would then work marginally at best. You also don't want 10 lbs going though the filter with that small restrictor, not because it won't filter, but it will be slow as molasses. Key is to move "x" volume of oil through a bypass filter in "y" amount of time given standards of oil pressures seen in most engines....my opinion.
At the winery we use a centrifugal pump to supply wine to a plate and frame filter housing. Because the pump is not positive displacement, but merely a spinning centrifugal impeller, we can "deadhead" and not create problems. We restrict the flow out of the pump with a butterfly valve and also one at the intake of the filter housing, to reduce the flow rate. We can see the flow rate by means of an in-line flow meter, something usually out of the realm of possibility in engine oil/fluids for consumers. We do not restrict the flow out of the filter and the only restriction is that which is in the line, and the head pressure in the tank itself. There has to be a negative differential pressure on one side of the filter pad or there will be no reason for wine to flow through. We also have pressure gages set up on the inlet and outlet sides of the filter housing (wine) By measuring the difference between these two gages we can determine, along with the lack of flow, that the filter pads are indeed blinded with material and either needs to be replace or back flushed to clear some of the debris.
Each of our filter pads is 248 inches square of filter media nearly 3/8" thick, and go down to either 5 microns nominal or .6 micron nominal. Take that times 20 (filter pads in a typical plate&frame filtering at our place) =4961 sq in of filter area. Imagine that for filtering oil!
The nice thing about engine filtration, though, is it pretty constant for the majority of time. When you are driving down the road past 35 MPH or so, your oil pressure is about where it's going to be and doesn't vary too much up or down. But, remember, pressure doesn't translate to flow, only restriction translates to flow. Restrict it "somewhere" and you can achieve better filtration. With those B50 orifices, that only allow so much flow though there, it would appear to me to not restrict the outlet delivery point too much or you will be fighting with getting sufficient oil through there on a continuum.
