Originally Posted By: SuperBusa
That is true, and probably what Gary is trying to say sometimes ... he kind of talks in "code", so it's hard sometimes to decipher without the magical decoder ring.
The bottom line is that the filter's PSID is a strong function of FLOW VOLUME through it ... not pressure on its inlet side. It only takes pressure to cause the flow. The more pressure applied on a fixed flow resistor (filter/engine circuit), the higher the flow becomes ... fluid dynamics 101.
It could very well be that even though you are seeing pretty high oil pressure that the flow rate is relatively small ... it all really depends on the flow resistance of your engine circuit and the pump output volume vs. engine RPM characteristics.
The bottom line is that you need to measure the filter's pressure drop while it's on the car and going through the paces to get the real story. If the flow rate is pretty large then it's possible the filter does go into bypass way more than you would like. If the flow rate is low enough due to the engine's flow circuit being pretty restrictive, then the filter PSID won't be very much and the filter probably hardly will go into bypass mode.
Only an accurate measurement of pressure before and after the filter (and knowing the bypass opening spec) will tell you what's really going on.
Yep, flow is what matters for any resistive element in the circuit. My undergrad deg is in EE (working on a PhD in ME right now), and the natural EE analogy would be that current equates to flow, a resistor equates to a filter, and voltage drop across the element equates to PSID.
- Zero current -> Zero voltage drop across resistor
- As current rises, voltage drop increases according to v = IR (ohm's law, probably some analogous law exists in fluids)
- Max voltage drop occurs at max current. Max current is limited by supply capabilities.
So if you put in a 2nd resistor in the circuit, in series, that is much larger than the 1st, it will limit the current through the entire circuit and become the governing factor for overall current flow. However, it doesn't guarantee that the voltage drop across the first resistor goes to zero or even that it becomes negligible.
So my sticking point with Gary's statments lies with his assertion that whether the oil pump is in relief somehow has an effect on how the filter behaves in response to a given flow through it.
I understand that the engine itself presents a much larger resistance to flow than the filter itself, that could easily justify why the PSID across the filter may become negligible. An easy way to verify would be to take pressure measurements post filter with a normal filter and with a gutted filter (no media). If what Gary is saying is true, then pressure would be negligibly different between the two scenarios. I'm sure someone has tested this before.
However, the impact of the oil's internal relief as Gary describes it still puzzles me. In an electric circuit, the analogue to a relief valve opening could be a short circuit from before the 1st resistor back to ground. With a little more thought, I think a better analogue would be another resistor run in parallel to the original one. This aligns with Gary's statements as well.
Originally Posted By: Gary Allan
The relief valve is in parallel with the filter engine circuit.
The net effect is that you have two paths with some resistance to flow along each. This represents a filter in bypass mode quite well. This means that the flow across the relief + the flow across the filter should add up to the total net flow of the pump.
So the question becomes, how much flow is the relief bleeding off? We know what the opening PSI of the relief is, but that tells us nothing about flow through it, which is what we'd need to know in order to determine flow across the filter and thus PSID across the filter. However, one thing is for certain, an open oil pump relief valve is not going to increase PSID across the filter with no other changes to the system. An open relief means that flow is being diverted, which means less flow through the filter and thus less PSID, again as long as nothing else in the system changes. I have trouble reconciling that with what Gary said here:
Originally Posted By: Gary Allan
"
The vast majority of elevated PSID instances are when the oil pump is in relief. Again, if the volume is high enough, you can tax the throughput potential of the filter ..and ONLY then will there be an elevated PSID that can even approach the instances of cold operation oil pump relief induced PSID. "
The only case where an open relief might result in elevated PSID is if the supply flow continues to rise at a rate faster than the relief can bleed it off. Then you have elevated flow through the filter and a rise in PSID across it. In practice, this must be what happens. The oil pump relief (in my case) is a fixed size outlet with a spring loaded valve. Once the valve is pegged fully open, the supply flow will continue to rise with engine RPM. However, the relief hole does not get any bigger, so pressure continues to rise on the supply side of both the oil filter and relief valve. This added pressure seeks to relieve itself and results in more flow through the relief and the filter. At some point, the flow rate through the filter reaches a point where the PSID across the filter opens the bypass for all flow rates equal to or greater than that threshold.
So really, what Gary is saying is true only if the relief valve is incapable of making flow constant. Most pump relief valves probably fall into this category.
Okay, I think I've got my understanding on firm ground now. It just puts an exclamation point on the fact that the PSI on one side of the filter or the other reveals nothing. What we need to know is FLOW, and that can be hinted at with PSID.
So in my case, because I have removed the oil squirters in the block, am using a thicker oil, and revving 1000+ rpm over what the pump was engineered for, my concern is that the higher than stock flow rate combined with the thickness of the oil at 9000+rpm is causing the bypass valve in the filter to hang open. The reason why this is worrisome is because if something does go wrong in the motor and metal shavings (say from a destroyed piston, something that won't typically happen on a cold start) are released into the oil while the bypass is open, the damage to the motor will be much greater than if the bypass was closed and full flow filtration was maintained.
In fact, a common modification to this motor in high rev applications is to use the S2000 oil pump, which flows less at a given engine RPM. This is because the S2000 pump was not designed to provide extra flow to feed the VTC (variable cam) system that was added on to the K-series motors used in the RSX-s.
Hopefully I'm worrying about nothing, but it's better to know than to think you know.