How to test opening PSI for oil filter bypass?

[chunky]

 Originally Posted By: ARCOgraphite

It appears that if the engine drill post filter is restrictive enough to limit max volume flow, the PSID may remain minimal even with a large operating pressure at high rpm. What's the can burst on the bosch?

That's exactly why I've got to get a 2nd gauge to figure out what the PSID pre/post filter is. I don't know the actual spec for can burst on the bosch, but I do know I have yet to burst one in 10k on this motor and 20k on a previous motor with a similar oiling setup.

 

[Gary Allan]

 Quote:

At max oil flow there is max filter PSID. When the oil flow is between zero and max, there is some corresponding filter PSID between zero and the possible maximum.

Nope. Outside of exceptional circumstances, the filter will mostly be undetectable in terms of PSID; through a very broad range of volumes. Now if you get your hot oil treatment going ..and get high enough volume to actually make the filter taxed for throughput potential ..then it may show itself.

 Quote:

f you use an oil filter that is pretty restrictive and has a pretty low bypass setting on an engine that has a high volume oil pump, then that filter could certainly go into bypass way before the oil pump goes into relief mode.

I'd restate that as being "at high enough volume". 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.

 

[SuperBusa]

 Originally Posted By: chunky

I'm leaning towards trying to find a filter that has a higher psi bypass as it would be easier than modding the oil pump. The factory manual specifies normal oil pressure as 80psi as measured from the stock oil pressure switch location. If I use a filter with a higher psi bypass, I'll just have to make sure that I'm still getting 80psi or better at the stock location.

The bypass setting of the filter will not have any influence on what the oil pressure will be downstream of the filter. The filter's restrictiveness will determine that ... but only when the oil pump is in relief mode. When the oil pump is not in relief mode, then all the oil from the pump goes through the filter/engine circuit (positive displacement pump), and you will not see any pressure reduction - even with a more restrictive filter. But, in pump relief mode, a more restrictive filter will show less oil pressure downstream of the filter than a better flowing filter would under the same conditions.

 

[SuperBusa]

 Originally Posted By: Gary Allan

 Quote:

At max oil flow there is max filter PSID. When the oil flow is between zero and max, there is some corresponding filter PSID between zero and the possible maximum.

Nope. Outside of exceptional circumstances, the filter will mostly be undetectable in terms of PSID; through a very broad range of volumes. Now if you get your hot oil treatment going ..and get high enough volume to actually make the filter taxed for throughput potential ..then it may show itself.

My statement is 100% accurate. It just may be that the "max" PSID is very small, depending on the combo of all the factors involved. It's 100% true that at zero oil flow the PSID is zero, and at max oil flow the PSID is max ... given that the viscosity doesn't change.

 Originally Posted By: Gary Allan

 Originally Posted By: Souperboosha

if you use an oil filter that is pretty restrictive and has a pretty low bypass setting on an engine that has a high volume oil pump, then that filter could certainly go into bypass way before the oil pump goes into relief mode.

I'd restate that as being "at high enough volume". 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.

Last time I checked, if you have a high volume oil pump and high RPM, then you most likely have high enough volume. Again, my statement is 100% accurate as stated ... you're just "parroting and twisting" it up.

 

[chunky]

 Originally Posted By: SuperBusa

The bypass setting of the filter will not have any influence on what the oil pressure will be downstream of the filter. The filter's restrictiveness will determine that ... but only when the oil pump is in relief mode. When the oil pump is not in relief mode, then all the oil from the pump goes through the filter/engine circuit (positive displacement pump), and you will not see any pressure reduction - even with a more restrictive filter. But, in pump relief mode, a more restrictive filter will show less oil pressure downstream of the filter than a better flowing filter would under the same conditions.

Hmm. After thinking about this a bit, here are my thoughts. I think I've had a somewhat short sighted view of what the bypass valve does. The bypass valve exists to ensure that flow requirements are met in case the filtration media imposes to great a restriction on the oil, be it b/c the oil is cold or the filter is clogged up. So the bypass PSI is selected by engineers based on the expected pressure drop across the filter media to cover most driving situations. The 13psi bypass that is typical of filters for the k20a2 is based on using 5w-30 oil and revving to 8000rpm with oil squirters installed. However, in my case, I'm using a heavier oil. The oil pump is a positive displacement pump, so it's moving the same volume of oil, but the pressure pre-filter is higher because the thicker oil does not move as freely through the filter media, especially at high flow volumes. Because the thicker oil does not flow as freely through the filter as a thinner oil, the PSID pre/post filter goes up. This can potentially result in the undesirable case of the bypass staying open more often than not. Clearly I don't want to give up oil flow, so modifying the relief in the oil pump may not be desirable as that results in part of the oil flow being diverted back into the pan. Finding a filter with a higher bypass PSI would ensure full flow filtration without giving up oil flow. However, the best option might be to find an even bigger filter so that even at high flow volumes, the PSID across the filter media doesn't exceed the 13psi of the stock spec bypass. I'm already using an oversize filter application (s2000 instead of rsx type-s filter), and I'm still seeing oil pressures that are quite high. My gauge has a peak memory feature and I've seen as high as 130psi recorded, but never seen a steady pressure of more than 110 as I reach redline. 110psi might be just fine so long as the post filter oil pressure is 100psi. So really, what I need to do is get on the ball and measure the PSID across the filter b/c the pressure on one side or the other doesn't tell me anything. It's the difference that matters.

 

[Gary Allan]

 Quote:

The bypass valve exists to ensure that flow requirements are met in case the filtration media imposes to great a restriction on the oil,

A bypass valve exists to prevent oil starvation. The bypass valve setting is to limit stress on the media (you can turn that inside out as needed - it will still work).

 Quote:

So the bypass PSI is selected by engineers based on the expected pressure drop across the filter media to cover most driving situations.

It's selected to limit the maximum resistance that the filter can present to pressurized oil flow. The expected pressure drop is next to nothing.

 Quote:

However, in my case, I'm using a heavier oil. The oil pump is a positive displacement pump, so it's moving the same volume of oil, but the pressure pre-filter is higher because the thicker oil does not move as freely through the filter media

More accurately you are developing more pressure due to higher viscosity oil and that will mean that you can't stay out of relief with that viscosity ..and THAT will cause routine elevated PSID. THEN filter resistance will be 100% apparent. Out of relief, it tends to be 100% (near 'nuff) transparent.

 Quote:

Finding a filter with a higher bypass PSI would ensure full flow filtration without giving up oil flow.

Unless you're exclusively talking about higher engine speeds, at higher pump output levels, a higher bypass valve setting will ASSURE reduced oil flow.

 Quote:

My gauge has a peak memory feature and I've seen as high as 130psi recorded, but never seen a steady pressure of more than 110 as I reach redline. 110psi might be just fine so long as the post filter oil pressure is 100psi.

What is your start up pressure ..at idle? Where does it sit before starting to react to warmed oil? That is, let's say you start @ 100psi ..but going down the road you watch it retreat to 85psi ..but never return to 85 at normal road speed (for grannies). That would tend to point to an 85 (or whatever) limit. Your viscosity at the time may force the pressure to exceed that limit ..but that would be the setting. UNTIL you're at that sensible volume/pressure relationship ..that no longer has the relief open, you are seeing reduced flow ..and elevated PSID. The PSID, IN THIS CASE, is 100% due to the pump being in relief. The pump is not in relief due to too restrictive a filter. The filter appears at its true restrictive property due to the pump being in relief. The reason the pump is in relief is since the engine cannot process the volume of oil at that rate, at that viscosity.

 

[chunky]

 Originally Posted By: Gary Allan

A bypass valve exists to prevent oil starvation. The bypass valve setting is to limit stress on the media (you can turn that inside out as needed - it will still work). It's selected to limit the maximum resistance that the filter can present to pressurized oil flow. The expected pressure drop is next to nothing. More accurately you are developing more pressure due to higher viscosity oil and that will mean that you can't stay out of relief with that viscosity ..and THAT will cause routine elevated PSID. THEN filter resistance will be 100% apparent. Out of relief, it tends to be 100% (near 'nuff) transparent. Unless you're exclusively talking about higher engine speeds, at higher pump output levels, a higher bypass valve setting will ASSURE reduced oil flow. What is your start up pressure ..at idle? Where does it sit before starting to react to warmed oil? That is, let's say you start @ 100psi ..but going down the road you watch it retreat to 85psi ..but never return to 85 at normal road speed (for grannies). That would tend to point to an 85 (or whatever) limit. Your viscosity at the time may force the pressure to exceed that limit ..but that would be the setting. UNTIL you're at that sensible volume/pressure relationship ..that no longer has the relief open, you are seeing reduced flow ..and elevated PSID. The PSID, IN THIS CASE, is 100% due to the pump being in relief. The pump is not in relief due to too restrictive a filter. The filter appears at its true restrictive property due to the pump being in relief. The reason the pump is in relief is since the engine cannot process the volume of oil at that rate, at that viscosity.

It seems highly improbable to me that PSID across the filter media will be next to nothing. Zero flow = zero PSID, but at higher flow rates, the simple friction of the oil moving through the filter media should impose an appreciable flow restriction. If PSID across the filter is next to nothing, then I'm worrying about the bypass PSI for nothing as it's function would be utilized exclusively during cold starts. Even in a straight pipe of sufficient length, with no obstructions, you will see a measurable PSID from one end to another due to frictional losses. I mean, I am not a fluids guy, but I'm having trouble accepting the idea that PSID across the filter media is negligible. I do agree that an oil filter with a higher bypass valve PSI should result in less flow under identical conditions to a filter with a lower bypass PSI that is in bypass mode. Startup pressure at idle is 90+ with oil that is 80-100deg. When hot the idle pressure comes down to 25-28psi with 200+deg temps. With the hot oil, I see pressures from 90-95, relatively independent of rpm. I see 90-95 from 3500-5000rpm. I think at that point the bypass in the pump is open. I don't understand why the oil pump going into relief mode would result in a PSID across the filter media. All the relief is doing is curbing the linear rise of oil flow. In the instant before the relief opens and the instant after the relief opens, the flow output of the oil pump is the same. And actually, as long as the oil flow characteristics through the motor do not change, the flow output of the pump will remain the same for any RPM while in relief. I really can't wrap my head around why the oil pump's relief valve opening causes a PSID across the filter. The filter should cause a PSID that is related to the flow rate across it, no matter if the oil pump is in relief or not.

 

[SuperBusa]

 Originally Posted By: chunky

Hmm. After thinking about this a bit, here are my thoughts. I think I've had a somewhat short sighted view of what the bypass valve does. The bypass valve exists to ensure that flow requirements are met in case the filtration media imposes to great a restriction on the oil, be it b/c the oil is cold or the filter is clogged up.

Yep ... true statement.

 Originally Posted By: chunky

So the bypass PSI is selected by engineers based on the expected pressure drop across the filter media to cover most driving situations. The 13psi bypass that is typical of filters for the k20a2 is based on using 5w-30 oil and revving to 8000rpm with oil squirters installed.

Most likely true. Filter engineer's design the bypass valve setting based on the engine specs and expected filter use duration (oil pump volume output performance, RPM, oil viscosity, expected OCI and media loading, etc). For instance, there is a reason Subaru specifies an oil filter with a 23 psi bypass valve ... the engine has a pretty high volume oil pump. And of course, the engineers have to assume the driver will at some time hammer the thing to redline now and then for more than a few seconds. I doubt the Subarus used in off road rally races use a filter with an 8-10 psi bypass valve.

 Originally Posted By: chunky

However, in my case, I'm using a heavier oil. The oil pump is a positive displacement pump, so it's moving the same volume of oil, but the pressure pre-filter is higher because the thicker oil does not move as freely through the filter media, especially at high flow volumes. Because the thicker oil does not flow as freely through the filter as a thinner oil, the PSID pre/post filter goes up. This can potentially result in the undesirable case of the bypass staying open more often than not.

Yes ... this has been my viewpoint also for sometime. Depending on the pump's volume output, the oil viscosity and the filter's design (flow vs PSID performance AND bypass valve setting) it is very possible that there is more filter bypass action going on then one would think. Of course, we can all sit around and theorize and debate if it can happen or not, and how often it happens ... but to verify it, one would have to actually determine the filter PSID under driving conditions with pressure measurements to validate the theory or not.

 Originally Posted By: chunky

Clearly I don't want to give up oil flow, so modifying the relief in the oil pump may not be desirable as that results in part of the oil flow being diverted back into the pan. Finding a filter with a higher bypass PSI would ensure full flow filtration without giving up oil flow.

My thought on this is if the oil pump relief pressure setting was increased, you will be getting higher oil flow volume up to and at the point where the pump goes into relief mode. From that point on, the input pressure to the filter/engine flow circuit is essentially fixed at the relief pressure ... and that also means the volume going through the filter/engine circuit is also fixed, and determined by the total resistance of the circuit. So, in other words, if the pump goes into relief at say 120 psi (after modification) vs. 90 psi (OEM setting), then there will be more volume going down the filter/engine circuit at the 120 psi relief setting than a the 90 psi setting. All the filter/engine circuit knows is that X psi is pushing oil through the circuit ... and the higher the input pressure is, the higher the volume is. On the extreme other end of the scale to drive home the example, if the pump relief was set to 20 psi then there wouldn't be much oil going down the filter/engine flow circuit, but most of the volume would be shunted back to the sump. But yes, it's true that if the oil pump relief setting was increased, then the oil filter would be even more likely to go into bypass mode due to the increased flow ... but, the total volume (flow through media + flow trough bypass) would be increased with a pump relief setting that is higher.

 Originally Posted By: chunky

However, the best option might be to find an even bigger filter so that even at high flow volumes, the PSID across the filter media doesn't exceed the 13psi of the stock spec bypass.

True ... more media surface area results in less total PSID across the filter with the same flow volume and viscosity.

 Originally Posted By: chunky

So really, what I need to do is get on the ball and measure the PSID across the filter b/c the pressure on one side or the other doesn't tell me anything. It's the difference that matters.

Agreed ... plus Gary and I want to see who's theory is right on if you're filter is in bypass more than one would imagine ... well, at least one of us.

 

[SuperBusa]

 Originally Posted By: chunky

It seems highly improbable to me that PSID across the filter media will be next to nothing. Zero flow = zero PSID, but at higher flow rates, the simple friction of the oil moving through the filter media should impose an appreciable flow restriction. If PSID across the filter is next to nothing, then I'm worrying about the bypass PSI for nothing as it's function would be utilized exclusively during cold starts. Even in a straight pipe of sufficient length, with no obstructions, you will see a measurable PSID from one end to another due to frictional losses. I mean, I am not a fluids guy, but I'm having trouble accepting the idea that PSID across the filter media is negligible.

Hummm ... I've already gone round and round about the whole fluid dynamics physics thing. All I know is just don't use the word Bernoulli around here. Your understanding is good ... any time there is flow and friction there will be a corresponding PSID. If the filter PSID is maximum at pump relief (that's when the pressure to the filter/engine circuit is highest), then it could also be said that the filter's PSID will be just a hair less then max when the oil pump is just a hair below relief pressure. Likewise, if if the pump pressure is somewhere between zero and relief pressure, then the filter's PSID will be somewhere between zero and max (viscosity is fixed in this example). The filter's PSID goes up correspondingly when the the pump's pressure and volume output go up. It can't be any other way.

 

[SuperBusa]

 Originally Posted By: chunky

I don't understand why the oil pump going into relief mode would result in a PSID across the filter media. All the relief is doing is curbing the linear rise of oil flow. In the instant before the relief opens and the instant after the relief opens, the flow output of the oil pump is the same. And actually, as long as the oil flow characteristics through the motor do not change, the flow output of the pump will remain the same for any RPM while in relief.

You see it the same exact way I do. You are right, the oil pump pressure relief is just controlling the maximum possible pressure put on the inlet to the filter/engine oil flow circuit. The amount of oil volume that will flow down that circuit will be determined by the oil viscosity and the fixed total flow resistance of the filter + engine circuit. Simple fluid dynamics concepts.

 Originally Posted By: chunky

I really can't wrap my head around why the oil pump's relief valve opening causes a PSID across the filter. The filter should cause a PSID that is related to the flow rate across it, no matter if the oil pump is in relief or not.

I can't either ... because it doesn't happen that way. It happens like both you and I describe. There is ALWAYS some PSID across the filter if there is flow across it. The exact amount of PSID across the filter is determined by these main factors - oil viscosity, flow volume and the fixed flow resistance characteristics of the filter element itself. Depending on the combination of these factors, it is possible to have the bypass valve open more often then desired.

 

[chunky]

Well, I have been hawking the web for awhile looking for another oversized oil filter application. I *think* I have found one in the form of the Purolator L30165. From the purolator website: Specifications: Anti-Drain Back Valve Yes Height 4.74 O.D. 2.98 Relief Valve P.S.I. 25-35 Threads M20x1.5-6H Type of Filter Spin-on This is for the Porsche 968, 1995 model year. There is also a wix and bosch part number for this type of filter. I'm 95% sure this thing will fit. If I do find that the bypass is hanging open in the higher revs, I'm going to give this filter a shot since it has the higher bypass PSI and is larger than my current filter, which would presumably reduce PSID across the filter to start with. Now, I just need to find the time to take some measurements. :)

 

[chunky]

 Originally Posted By: SuperBusa

Agreed ... plus Gary and I want to see who's theory is right on if you're filter is in bypass more than one would imagine ... well, at least one of us.

No one is more curious than me. I want to make sure I'm not running a setup that is in bypass all the time when I hit the track with this car. A road course means 6000+rpm pretty much the entire time.

 

[chunky]

Oh, I think I just wrapped my head around something. If there is something more restrictive than the filter just downstream from the filter, then there will be almost no PSID across the filter media. The more restrictive element will be the governing dynamic. However, in that case the bypass would virtually never open.

 

[SuperBusa]

 Originally Posted By: chunky

Oh, I think I just wrapped my head around something. If there is something more restrictive than the filter just downstream from the filter, then there will be almost no PSID across the filter media. The more restrictive element will be the governing dynamic. However, in that case the bypass would virtually never open.

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.

 

[Gary Allan]

 Quote:

It seems highly improbable to me that PSID across the filter media will be next to nothing. Zero flow = zero PSID, but at higher flow rates, the simple friction of the oil moving through the filter media should impose an appreciable flow restriction. If PSID across the filter is next to nothing, then I'm worrying about the bypass PSI for nothing as it's function would be utilized exclusively during cold starts.

Correctly stated ..it's improbable to you that the filter has no appreciable resistance in the entire circuit. What you're failing to factor is that, out of relief, the filter must be subordinate to the engine in ratio of total resistance to flow. In our case, with a dedicated flow (not in relief), the engine and filter will maintain a relative ratio between each other. The engine presents a very high resistance. The filter is a fraction of that. Once the relief is open, then that no longer applies. Now you don't have to maintain that ratio. Now you have a garden hose, a faucet ..a wall outlet. The relief valve is in parallel with the filter engine circuit. This introduces a reactive component to the equations. Since fluid has no choice in a non-relief scenario, you're looking a the fluid accelerating through any restrictions that it may encounter. For example ..bumper to bumper traffic transitioning from 2 lanes to 4 lanes and back to 2 lanes. The rate of cars/min. is unchanged, they either accelerate or decelerate at the change in cross-section of the conduit that they're in. ..but again, "at higher flow rates" is your focus. Why focus on "higher flow rates" when being concerned about bypass activity ..when you'll encounter the MOST bypass potential activity at cold start with mismatched viscosity??? This is the point I'm trying to get across. WHAT RISK ARE YOU TRYING TO AVOID AT 8000rpm THAT YOU WON'T ENCOUNTER EVERY START UP AND PROBABLY FOR LONGER DURATION?? Go to a 40 or 30 grade oil to "fit" more of it through the engine. This is the principle cause of elevated PSID due to inordinate pump relief events. Filter media can be expressed as a mass of orifices. At some point (in Supaboosah's oil oil ultra high volume scenario) they do produce a disproportional resistance to flow that straight forward resistive elements do not.

 

[chunky]

 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. :)

 

[chunky]

Thanks again for all the responses, everyone has been very helpful here.

 

[SuperBusa]

 Originally Posted By: Gary Allan

 Quote:

It seems highly improbable to me that PSID across the filter media will be next to nothing. Zero flow = zero PSID, but at higher flow rates, the simple friction of the oil moving through the filter media should impose an appreciable flow restriction. If PSID across the filter is next to nothing, then I'm worrying about the bypass PSI for nothing as it's function would be utilized exclusively during cold starts.

Correctly stated ..it's improbable to you that the filter has no appreciable resistance in the entire circuit. What you're failing to factor is that, out of relief, the filter must be subordinate to the engine in ratio of total resistance to flow. In our case, with a dedicated flow (not in relief), the engine and filter will maintain a relative ratio between each other. The engine presents a very high resistance. The filter is a fraction of that. Once the relief is open, then that no longer applies. Now you don't have to maintain that ratio. Now you have a garden hose, a faucet ..a wall outlet. The relief valve is in parallel with the filter engine circuit. This introduces a reactive component to the equations.

The following fact that I’m going to describe is very important to grasp in order to see that it's possible to cause an oil filter go into bypass mode if the right conditions are present -- i.e., high oil flow rate, thicker oil used, wrong filter with low bypass setting and/or too restrictive filter is used. When the oil pump goes into relief mode, the oil flow volume through the filter/engine circuit is at its ("theoretical") maximum (for the oil viscosity at that time) – even while the pump is in relief, and stays at that maximum flow volume until the pump goes out of relief. I say "theoretical" maximum, because as Chunky as mentioned above, if the pump relief valve/circuit can't keep up with the required relief volume in order to maintain a constant pump outlet pressure, then the pressure will rise above the relief setting and cause more oil flow volume to the filter/engine circuit than if the relief held exactly at the set relief pressure. Pump output pressure against the fixed resistance to flow (filter/engine circuit) determines the volume of oil that will go down the flow path. Note - assume the oil viscosity is always constant in these examples, as the oil viscosity is a big factor on what the volume is when the pump goes into relief. We are just looking at what’s going on when the pump pressure increases and then goes into relief mode. The PSID ratio between the filter and engine circuits does not change if the pump goes into relief mode. All that happens is that the pressure and flow volume at the inlet to the filter/engine flow circuit is limited to a constant based on the pump's relief valve setting. If the oil pump goes into relief at 90 psi, then there will a constant 90 psi on the filter/engine circuit inlet, and the oil volume that will naturally go through that fixed resistance will be X gpm and never change as long as the oil viscosity stays constant and the inlet pressure is constant at 90 psi. As soon as the pump goes out of relief, that means the pressure has dropped below 90 psi, and that also means that the oil flow volume has decreased accordingly. Again, the viscosity is assumed constant here. If the engine has a relatively low resistance flow circuit, and a high volume oil pump, then there could still be a pretty good volume of oil going through the filter/engine circuit – even before the pump goes into relief mode. The Subaru engines are supposedly pumping something like 12 gpm at max output ... if you put a filter with a bypass valve set too low, then you could see much more filter bypassing action than desired due to the fact that the filter could go into bypass before pump relief occurs. This is the exact scenario that Chunky is concerned about. Since he has the OEM oil pump, I’m not too sure what it’s gpm rating is, but from the data he’s given in this thread it seems there could be a pretty healthy flow rate based on the oil pressure he’s seeing. Again (as I’ve stated before), the ONLY real way to know is to measure the delta P across the filter under actual racing conditions on the track.

 Originally Posted By: Gary Allan

Since fluid has no choice in a non-relief scenario, you're looking a the fluid accelerating through any restrictions that it may encounter. For example ..bumper to bumper traffic transitioning from 2 lanes to 4 lanes and back to 2 lanes. The rate of cars/min. is unchanged, they either accelerate or decelerate at the change in cross-section of the conduit that they're in. ..but again, "at higher flow rates" is your focus. Why focus on "higher flow rates" when being concerned about bypass activity ..when you'll encounter the MOST bypass potential activity at cold start with mismatched viscosity??? This is the point I'm trying to get across. WHAT RISK ARE YOU TRYING TO AVOID AT 8000rpm THAT YOU WON'T ENCOUNTER EVERY START UP AND PROBABLY FOR LONGER DURATION?? Go to a 40 or 30 grade oil to "fit" more of it through the engine. This is the principle cause of elevated PSID due to inordinate pump relief events. Filter media can be expressed as a mass of orifices. At some point (in Supaboosah's oil oil ultra high volume scenario) they do produce a disproportional resistance to flow that straight forward resistive elements do not.

As mentioned above, if the operational conditions are right, it’s entirely possible to have unwanted filter bypass events even with hot oil. If Chunky uses a larger filter (less restrictive) with a higher bypass setting, then it will give him much more headroom to prevent bypass mode on the track, as opposed to running a little tiny filter with a low bypass valve setting. That’s why they make filters different for racing purposes ... because those conditions are most likely outside the normal operational envelope for most filters used on Grandpa’s Oldsmobile.

 

[SuperBusa]

 Originally Posted By: chunky

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.

Don't confuse the oil pump going into pressure relief mode vs. the oil filter going into bypass mode. They are NOT related in any way. If the oil pump volume and oil viscosity is high enough before the pump ever goes into pressure relief, it's still possible to see the filter go into bypass mode. If the oil pump goes into pressure relief mode when there is a pretty small oil flow volume, then the filter bypass will probably hardly ever (maybe on extreme cold starts) or never go into bypass mode - as I said before, you could have high oil pressure and a relatively low flow rate depending on the resistance of the filter/engine circuit. Obviously, the performance characteristics of the oil pump and it's pressure relief setting are very important factors to this whole discussion. Think of the oil pump as a voltage/current power supply. The pump's relief valve is like setting a voltage limit on the PS. If you put a max voltage across a fixed resistance you get a corresponding max current. The pump when in pressure relief mode is "ideally" trying to hold the oil pressure at a max constant, which in turn limits the flow volume to a max constant (assuming flow resistance and oil viscosity is constant). All the pump pressure relief valve does in LIMIT the pressure being applied to the filter/engine circuit. As said before, depending on the oil viscosity, that applied pressure will determine how much of the pump's volume goes down the filter/engine circuit ... any excess volume output of the pump MUST go back to the sump via the relief valve circuit. I would imagine that most pump relief valves are low resistance to flow ... but even in your case it sounds like it can be "overpowered" by the pump and not relieve the excess volume 100% efficiently. That's when you see pump output pressure higher than the relief valve psi setting.

 

[Gary Allan]

 Quote:

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.

The relief valve and the bypass valve are reactive components. The engine is a static linear resistive element. The engine will ALWAYS be a product of out traditional adaptive Ohms law equations. It's got on impedance factor to it. You pump x volume @ y visc ..you get P. This never changes at all under any circumstances. NEVER. Keep that in mind ..or see if Superbusa can convince you otherwise. Baloney can't argue with that one. Can we agree on a number of givens? Can we agree (super doesn't need to agree - he'll attempt to load on "riders" that will confound discovery ) That the engine will be a linear model under any circumstances that we will discuss here. ???? Let's just take this one element at a time in "construction". I'm trying to limit the dissertations.