Rex, you are right. In my memory I thought it was a 2% improvment, but I went and checked my records. Only 1.5% improvment. That made the gains I saw only 6-9 hp. As far as the filter is concerned my testing used the same filter (A-B-A test) so that part of your reply dosen't fit in this test.
As far as the pump bending.... really? The Dailey pump tested has bearing supports at every stage along with dowels to align the sacvange and pressure sections so there not likely to be any gear rub in the housings unlike say a Weaver pump. Also the pump I use has an internal manifold but still preforms better with dual -16 returns.
The math you supplied is great and you're right as the pump I run puts out < 7 gpm at less than 80 psi. so using your formula would be right. On the other hand maybe my testing was done correctly and I'm seeing the improvments that your "calculations" say I can't be making. Van Dyne may have seen other numbers on his dyno but Stewart builds different engines than I do, and builds them in a different style so if you're using that as a basis for this discussion I'd say that's why we race.
Now getting back to the filters. I clam no advanced knowledge on the subject, I just posted what I saw on my dyno and what setup I like to run in my and my customers cars and the reason I do so. If you can look at the inspection filter and see a problem before it become's major your can save yourself many more dollars from an engine failure than worrying about the cost of rebuilding your oil pump and cleaning the tank.
One last note to those reading this and making their own decisions on which way you want to plumb your oil system. Keep in mind it's very easy to get an idea what your inspection filter is telling you. I open the filter and spray it off with brake kleen onto a clean white paper towel. I use a loop or at least a 5x power magnifier and look at what comes out of the filter. If you do this after every pass you will some iron dust, you can tell with a magnet. Small aluminum specks can be the springs rubbing on the heads. The valve springs also make little specks or splinters from the titanium retainers. Any flakes of aluminum or copper should let you know that it's time to stop and look a little deeper. I found some little white plastic type slivers one time before a Trans-Am race, I dodn't know what it was but as I thought about it I realized it was from a valve seal. How did it get there? Broken valve spring! Save the race for us, finished 2nd at Mosport that day.
I just pulled the engine from my Modified roadster and took a picture of the pump. This is what I run currently, 5 stage Dailey pump, Fram HP6 (I know they're junk
) filter before engine iol in, and a low restriction scavange return filter of 80 microns. The oil pan does have a very corse screen to keep any big chunks ( like a failed lifter) from jamming the pump and stopping it.
I don't like to make long reply's normally and that leaves the door open for other interpretations. I hope this fills in some of the blanks I my have left out of the original responce. I also wish my memory was better so I would't get other people jumping out of their chair saying BS.
Lots of different ways to skin a cat. This is mine, not wrong, just different.