Quote:
Originally Posted by KillerBMotorsport
FSome call it a regulator, some call it a bypass. It's the same thing.
It does not open at 140psi.
Here's a plot showing oil pressure. Where the ramp rates change is where the bypass just cracks open and starts regulating. I would call it 75psi... which coincidentally, it right in line with 95% of the other oil pumps Subaru uses. The reason pressure keeps climbing after the bypass opens is because flow is increasing, further compressing the bypass spring, requiring more pressure to keep it open enough for the additional flow. Eventually what can happen is the bypass will aerate (if you have too big of a pump and an engine not made for it, for example), because flow out the bypass is horribly turbulent. Think of water coming out of a hose with your thumb covering the end. If you run too big of a pump AND shim it to increase pressure, then that inner rotor usually lives a short and violent life.
Flow is linear with RPM through the rotors (assuming constant temp and no AVCS). The bypass valve regulates the pressure and flow actually going into the engine.
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I've read here that shimming the spring makes no difference. Also, with your mode of operation, especially considering the flow rate of the pump, it should compensate for viscosity (temp). It doesn't seem to.