[poncho-mike]

While we're on the topic of oil pumps and Pontiac lubrication systems, I've always made some basic assumptions about Pontiac lubrication systems that may not be correct.

As I already mentioned, the Pontiac oil pump is a gear style positive displacement pump. The pressure coming out of the pump is regulated by a valve internal to the pump that limits the maximum oil pressure. I believe it may be possible to exceed that pressure under certain cases (such as a fully plugged filter or something blocking blocking the oil flow). At idle, the engine isn't pumping enough oil to exceed the oil pump pressure setting. As engine RPM increases the flow volume, pressure will rise to where the pressure is limited by the oil pump pressure valve . The oil leaving the pump goes into the oil filter adapter. There is a bypass valve in the oil filter adapter that will divert oil past the filter when pressure gets high enough due to high RPM or a restricted oil filter. At higher RPM, the oil from the oil pump bypasses the filter almost entirely. I think Pontiac engineering did this because they knew some car owners would let their oil filters get dirty, and they felt it safer to bypass the filter than to let the engine starve for oil.

What I don't know is how the bypass pressure setting in the oil filter adapter compares to the oil pump pressure setting. I always assumed that a standard production engine with a 45 psi oil pump was paired with an oil filter adapter that was set to bypass at a pressure slightly higher than the pump pressure. I also assume that an engine with a 60 psi pump has a different oil filter adapter than an engine with a 45 psi pump. What that meant to me was that when I rebuilt an engine and installed a 60 psi pump, I would replace the stock oil filter adapter with one from an engine that came from the factory with a 60 psi pump (Ram III, 70 455HO, etc).

The implication is this: If you put a 60 psi pump into an engine that originally came with a 45 psi oil pump, the pressure of the oil coming out of the oil pump might be higher than the pressure setting of the bypass valve, so you would be constantly bypassing the filter at anything above idle.

The alternative to that is that Pontiac engineering set the bypass pressure in the oil filter adapter high enough that it would work with a 45 or a 60 psi oil pump. That means there would be no difference between the oil filter adapter for an engine with a 45 psi pump vs a 60 psi pump.

Does anyone on this board know the answer to this question?