<<  In cruise if I then increase the throttle above 5000 rpm,
 > > > the pressure will slowly drop down to 40 again, over
 > > > a period of a few minutes.  Reduce the throttle, pressure
 > > > recovers to 80 in a few seconds.  Any ideas? >>

I have an idea. The oil is foaming. When it gets a load of foam in it, a
suction vortices
can form quickly. When the pump RPMs are high the vortices forms and the pump
looses effectiveness and the pressure goes down. When you power back, the
pump demand goes down, The vortices dies and the pump starts working better
again. Racing oils have more antifoaming agents to help prevent this problem.

I included a drawing of the best baffle I came up with for the wet sump race
engine.
The drainback hole is good for side loads and braking. For aircraft use, I
think that the hole should be more round. Anyway the idea is that the oil (or
a lot of it) ends up on top of the baffle and burps most of the air out
before it falls into the hole. I ran the oil level about 1/4" above the
baffle. If you put in too much, it blows out into the catch tank. The most
oil returns through the center cast iron, so that center hole gets most of
it. The oil with the most air tends to remain on top. If you try this design,
go slow and watch the oil pressure.
Lynn E. Hanover.

 
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