Z06:
Honestly, our oil pump is too good, see post below:
I have an idea for the oil-pump, just not enough time currently to pursue it...
The issue is flow rate. The 944/951 oil pump has too much flow. This might seem counter-intuitive, but let me explain:
The oil pump gerotor design is a positive-displacement pump. Doubling the RPM, ideally, doubles the amount of flow. In the 944/951, we have abnormally high oil-pressure at low RPMs, most vehicles will run 10-15psi per 1000rpm; yet, we have nearly double that pressure. Below the relief pressure, all the oil is getting pumped into the engine. However, once the maximum pressure is reached, excess oil is bypassed back into the oil pan. In our cars, after 2-3k RPM, maximum pressure is reached, and any extra pressure (flow) is diverted to the pan. So if the pressure is being diverted at 3k rpm, then doubling the RPM to 6k essentially doubles the flow. But for the most part the engine cannot use the extra flow, so all this extra oil flow is simply being diverted to the pan... At some point, the inlet flow requirements to the pump become greater than the passageways can flow (without aid), and the pump cavitates.
So the solution? Reduce how much the oil pump flows per revolution. What we don't want to do is restrict flow - reduce is not synonymous with restrict... The ideal solution would be to change the gerotor gear to one that simply flows less. In this case, at idle instead of having ~2bar oil pressure, we might only have 1bar. But, the oil pump will not have to bypass oil until a higher RPM, meaning it requires less inlet oil flow, and therefore not cavitating until a higher RPM than the stock pump.
By the way, I previously posted an incorect opening pressure for our OPRV, which is at 5 bar.