23psi bpv oil filter for WRX?

Posted by: 94exa2

23psi bpv oil filter for WRX? - 01/13/14 10:12 PM

Hey guys, I have done some reading, and it seems that my car (05Wrx) or most Subaru's in general "need" an oil filter with a 23psi bypass valve in it, due to the relatively high volume and pressure of the oem Subaru oil system.

From the research I have done, it seems almost all major oil filter manufacturers (Wix, Bosch, Mobil1, K&N, Fram etc) offer us filters with 8-12 psi bypass valves, meaning oil would bypass the filter most of the time.

Supposedly Purolator makes a filter for us with 16 or 18 psi bypass valve, I believe.

It seems like the "older" "black" oem Subaru filters were of better quality than the newer "blue" oem filters (made by Honeywell...Fram?) But seems impossible to find.

Are there any good non-oem oil filters that offer 20-23 psi bypass valves in them?
Anyone know where to find the black Subaru filters?

I have read that 09? and newer Mazda Rx8's used the same filter as the earlier black Subaru filters, just with Mazda on it. I also read '12? and new H6 Subarus do as well. But I have no Idea.
Posted by: sjstangman

Re: 23psi bpv oil filter for WRX? - 01/13/14 10:19 PM

PL14460
Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/13/14 11:17 PM

Purolator says its 14-18 Psi with anti drain back valve.

I want one with 23 psi and Im pretty sure the adb valve is pointless the way the filter is mounted.
Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/13/14 11:44 PM

K&N says 11-17 for their hp1008.
Seems to be same for M1108 and others.


I have read a bunch of people saying the blue Fram Subaru filters seem to leak at the gasket, and have very thin, weak canisters with [censored] filter material. But, has correct 23psi bpv.
I have read a bunch that the earlier black Tokyo Roki? filters are stronger, have better filter media and higher quality overall but were replaced with the blue Fram.

But, I have read that new Subaru's are using Tokyo Roki? filters, but, I have no confirmation if they do, or if the are right for my engine. Which I would love to know. I would also love to know if any retailer has 6 or 12 TR black Subaru filters.
Posted by: tenderloin

Re: 23psi bpv oil filter for WRX? - 01/13/14 11:50 PM

http://www.wixfilters.com/Lookup/PartDetails.aspx?Part=57712

http://www.framcatalog.com/PartDetailWindow.aspx?b=F&pn=PH9715

Concerning the "blue" filters Fram did have a very small recall on them. I have been using them on my sons Impreza with no problems at all.

http://www.fram.com/media/20698/recall_notice_02052013_for_distribution.pdf
Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/14/14 12:45 AM

Yeah I did read about the recall on the blue filter. As well as quite a few reviews about them leaking, and having poor filter element and weak/cheap construction.

I really REALLY wish I could find 12 oem Subaru Tokyo Roki oil filters.

Or knew much more about the Rx8 TR and newer Subaru H6 TR filters. I have read that they thread on just fine and have the 23 psi bpv, but don't know if "bigger" means longer, or larger diameter making it really close to the exhaust manifold.

Also read Subaru BRZ has Tokyo Roki filters that should fit.
Posted by: rrounds

Re: 23psi bpv oil filter for WRX? - 01/14/14 12:56 AM

The pressure that the oil pump puts out has nothing to do with PSID(bypass). My S2000 runs 85+ oil pressure going down the freeway and I run a 14 lbs bypass filter. My motorcycle runs over 100 lbs of oil pressure and its filter has 10 or 12 lbs bypass filter.

ROD
Posted by: tenderloin

Re: 23psi bpv oil filter for WRX? - 01/14/14 01:17 AM

Why not the Wix 57712? You can buy a dozen for about $5+ a piece delivered Meets the specs you are looking for and are top filters

By-Pass Valve Setting-PSI: 23
Anti-Drain Back Valve: Yes
Beta Ratio: 2/20=2/20
Burst Pressure-PSI: 300
Max Flow Rate: 9-11 GPM
Nominal Micron Rating: 21
Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/14/14 01:17 AM

There is a reason Subaru specifically spec'd their filters to 23psi instead of 8-14 like most oil filters. I do not want to be driving around with my oil bypassing the filter because I bought the wrong filter. I am looking for a good (better than oem Fram) oil filter with 23 psi bypass valve.

My first choice is the old 15208aa100 Subaru Tokyo Roki, but I cant find those anymore.

I would like information on the oem Rx8 To Ro filter, Subaru H6 To Ro filter, and Subaru Brz To Ro filter, pertaining to my 05 Wrx.
Posted by: ZeeOSix

Re: 23psi bpv oil filter for WRX? - 01/14/14 01:45 AM

Originally Posted By: 94exa2
Purolator says its 14-18 Psi with anti drain back valve.

I want one with 23 psi and Im pretty sure the adb valve is pointless the way the filter is mounted.


If Purolator specs that oil filter for that engine, then they have taken into consideration the performance characteristics of the oiling system ... ie, the oil viscosity used and the max flow volume of that engine to determine what the expected max delta-P is across their filter with loading factors included. All of that is used to determine what the by-pass valve should be set at.

If you compare every oil filter that is specified for that engine, they will not all have a 23 PSI by-pass valve like the Subaru OEM. That's because the design of the filter itself is also a factor on where the by-pass valve is set - ie, how the filter flows, how much media and what type of media is has.

If you are paranoid that an aftermarket filter maker didn't design their oil filter correctly that is specified for that engine, then stay with the OEM filter.
Posted by: 901Memphis

Re: 23psi bpv oil filter for WRX? - 01/14/14 02:24 AM

Wix is what you want. It's been discussed here before. Tenderloin already beat me to it. It's one of your best choices.
Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/14/14 02:36 AM

The little Wix? I guess I could get them a try if all else fails.

If I can find a case of the older oem Subaru Tokyo Roki oil filter I would buy those. If the Rx8 Tokyo Roki filter is the same as the one that used to be for the Wrx with 23psi I might go that route. If there are any other Subaru's that use oem Tokyo Roki filters that are suitable for my Wrx, I might got that route.

I just really want to stay with 23 psi as per Subaru.
And always hear/read oem To Ro is much better than oem Fram.
And heard/read those are the only two options with 23psi.
Until now, I guess Wix finally wised up and made one as well.
Honestly don't know why it's hard to find the correct one, other than the $5 cardboard Fram. (Mobil, Purolator, K&N, etc should, since there does seem to be a demand for them)
Posted by: 901Memphis

Re: 23psi bpv oil filter for WRX? - 01/14/14 06:35 AM

Maybe this thread will be of help, but i didn't ready all of it.

Previous Wix Thread
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2506579&page=all


Also this thread has a chart in it with PSID

http://forums.nasioc.com/forums/showthread.php?t=2301839&page=2
Posted by: tenderloin

Re: 23psi bpv oil filter for WRX? - 01/14/14 10:07 AM

Originally Posted By: 94exa2
The little Wix? I guess I could get them a try if all else fails

)


Not sure why the "little" Wix comment? If you are describing the diameter, I was told the filter was spec 'd smaller because where it sits. On our 07, it is completely surrounded by exhaust pipe. You literally fit your hand/wrench in between almost a circle of pipe. The larger diameter filters were too close to the exhaust, heating up the filter/oil so Subaru went to a smaller diameter filter rather than the trouble of moving where the filter is located.
Posted by: sjstangman

Re: 23psi bpv oil filter for WRX? - 01/14/14 10:46 AM

Originally Posted By: 94exa2
Purolator says its 14-18 Psi with anti drain back valve.

I want one with 23 psi and Im pretty sure the adb valve is pointless the way the filter is mounted.


My link says 20-25 without the valve:
http://www.purolatorautofilters.net/resources/Popup/Pages/PartDetailPopup.aspx?partnum=pl14460

Where did you get your info?
Posted by: ZeeOSix

Re: 23psi bpv oil filter for WRX? - 01/14/14 11:34 AM

Originally Posted By: 901Memphis

Also this thread has a chart in it with PSID

http://forums.nasioc.com/forums/showthread.php?t=2301839&page=2


Post #45 quote: "Be careful with BITOG, there are lots of people who think they know what they're talking about."

Humm ... wonder if he's a member here?
Posted by: ZeeOSix

Re: 23psi bpv oil filter for WRX? - 01/14/14 12:38 PM

Post #57 in the Nasioc forum linked above:

"Well, 25-27 psi is really close to 23, so that's a pretty small difference. Since pressure drop is a serial phenomenon, there would potentially be less pressure at the bearings and less pressure available to operate the AVCS. I stress potentially though, that would only be true when the filter was close to bypassing."

He doesn't realize that with a positive displacement oil pump (key to the discussion), the flow and pressure throughout the system is still the same, even if there is a larger pressure drop across the filter. What a more restrictive filter does do however, is make the pump output pressure increase accordingly to maintain the same flow and pressure in the engine, and this puts the pump closer to its pressure relief setting. But a more restrictive filter doesn't reduce the flow or pressure to the bearings up to that point.

The only time there would be a reduction of flow and pressure to the bearings is when the oil pump has hit pressure relief and the filter's restrictiveness has caused reduced flow due to increased resistance - as compared to a less restrictive oil filter.

The only reason I can see why Subaru uses such a high bypass valve setting is because their filter must be somewhat flow restrictive, and that combined with a high volume oiling system, and what ever factor they have thrown in for debris loading, causes the bypass setting to 23 PSI.

As I said earlier, if a filter manufacturer has specified a filter for a Subaru application that normally uses an OEM filter with a 23 PSI bypass setting, then the reason the aftermarket filter has a lower setting is probably because it flows better, and maybe they didn't put such a large safety margin on the bypass setting for debris loading, etc.



Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/14/14 02:06 PM

http://www.purolatorautofilters.net/reso...X&year=2005

They both say 14-18 psi to me. Maybe they change their website when I look it. If their site say 14-18 when I look, I don't want it.
Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/14/14 02:08 PM

Originally Posted By: ZeeOSix


As I said earlier, if a filter manufacturer has specified a filter for a Subaru application that normally uses an OEM filter with a 23 PSI bypass setting, then the reason the aftermarket filter has a lower setting is probably because it flows better, and maybe they didn't put such a large safety margin on the bypass setting for debris loading, etc.





"Higher flowing", as in, in bypass mode constantly? I could see that flowing alot more than actually going through the filter media...
Posted by: ZeeOSix

Re: 23psi bpv oil filter for WRX? - 01/14/14 02:54 PM

Originally Posted By: 94exa2
Originally Posted By: ZeeOSix

As I said earlier, if a filter manufacturer has specified a filter for a Subaru application that normally uses an OEM filter with a 23 PSI bypass setting, then the reason the aftermarket filter has a lower setting is probably because it flows better, and maybe they didn't put such a large safety margin on the bypass setting for debris loading, etc.


"Higher flowing", as in, in bypass mode constantly? I could see that flowing alot more than actually going through the filter media...


I'm talking about a "higher flowing" filter with the bypass valve always being closed. When oil flows through the media, it causes a pressure difference ("PSID" or "delat-P") across the filter. Here's an example of how the delta-P increases with increased oil flow while keeping the viscosity constant.

http://www.bobistheoilguy.com/forums/ubb...451#Post1619451

Variables that effect how much delta-P is produced across an oil filter are:
1) Flow performance per square inch of the media.
2) Total square inch area of the media (as area goes up, delta-P goes down if everything else is constant).
3) Oil flow volume.
4) Oil viscosity.
5) Debris loading rate vs. filter change interval.

All of these factors are considered when the filter designer comes up with a filter's bypass valve setting.
Posted by: sjstangman

Re: 23psi bpv oil filter for WRX? - 01/14/14 03:57 PM

Originally Posted By: 94exa2
http://www.purolatorautofilters.net/reso...X&year=2005

They both say 14-18 psi to me. Maybe they change their website when I look it. If their site say 14-18 when I look, I don't want it.


Your link is for the 14612. I linked to the 14460... completely different filters.

Based on this link it should fit the 2005 but not the 2006 and up.
http://forums.nasioc.com/forums/showthread.php?t=2148430
Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/14/14 09:41 PM

Originally Posted By: sjstangman
Originally Posted By: 94exa2
http://www.purolatorautofilters.net/reso...X&year=2005

They both say 14-18 psi to me. Maybe they change their website when I look it. If their site say 14-18 when I look, I don't want it.


Your link is for the 14612. I linked to the 14460... completely different filters.

Based on this link it should fit the 2005 but not the 2006 and up.
http://forums.nasioc.com/forums/showthread.php?t=2148430



I just went to the Purolator website and put in 2005 Subaru Wrx, and those are the filters they suggest. Not the correct bypass valve so I will pass.

I guess I am looking for more information on the new Subaru H6 Tokyo Roki, and newer Mazda Rx8 Tokyo Roki oil filters. Or a source to get the older oem Subaru TR oil filters meant for my car lol.
Posted by: tenderloin

Re: 23psi bpv oil filter for WRX? - 01/15/14 12:23 AM

It appears the TR filter that is for the S2 RX8 is N3R1-14-302. y Pass rating is 20.326.1 PSI About $10+ ea. with crush washers (pack of 6) delivered (2 places I checked) Filter is longer
Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/15/14 02:08 AM

Originally Posted By: tenderloin
It appears the TR filter that is for the S2 RX8 is N3R1-14-302. y Pass rating is 20.326.1 PSI About $10+ ea. with crush washers (pack of 6) delivered (2 places I checked) Filter is longer


Do you know of any Tokyo Roki filters that could be bought from Subaru other than the (larger diameter) H6 filter? I would love a TR of the correct size, instead of being much fatter or stick down to far from being to tall. And needs 23 psi bypass valve..
Posted by: 901Memphis

Re: 23psi bpv oil filter for WRX? - 01/15/14 03:43 AM

The Wix has the correct 23 psi bypass valve, why aren't you considering it?
Posted by: Eddie

Re: 23psi bpv oil filter for WRX? - 01/15/14 07:24 AM

WIX has the correct filter as 901 states. Is it possible that the NAPA GOLD for the WRX is the same?
Posted by: 05foresterXT

Re: 23psi bpv oil filter for WRX? - 01/15/14 12:30 PM

Originally Posted By: Eddie
WIX has the correct filter as 901 states. Is it possible that the NAPA GOLD for the WRX is the same?


He's apparently hung up on the size of it. The same recommendations were made on nasioc, but he doesn't want to use the "tiny" wix filter, but only wants the tokyo roki filter that's discontinued here, or info on whether the RX8's big tokyo roki filter will work.
Posted by: tenderloin

Re: 23psi bpv oil filter for WRX? - 01/15/14 01:59 PM

Cannot help much more than we have . Wix/Napa is perfect for his car. Good quality, right specs, priced right..easily found..but? Size which is fine for one model year later tha his is an issue? . Same with Mazda S2 RX8 filter that he inquired about. Helped with the research, found that it fits, although longer.Right spec;s he was concerned about. Found out pricing...Now seemingly only, wants something that hasn't been made in years. Oh well.
Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/15/14 02:56 PM

I'm not hung up on the size. Same size as oem Subaru blue filter right?
IF I can find the correct To Ro filters before my next oil change I will buy those.
IF one of the other Subaru Tokyo Roki filters (that seem to still be bought from the dealer) would work perfect, I would consider those. Same with Rx8.

Apparently the correct size Purolator has the wrong bypass valve, and the Purolator with the correct bypv is to0 large (diameter).

So Wix 57712 is really the ONLY non-oem oil filter with the correct 23psi? Would I be smart to trust Wix over Fram? lol

I've read quite about about the Wix having a very small filter media, and not being able to flow enough for the Subaru oil pump.
Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/15/14 03:11 PM

Originally Posted By: tenderloin
Cannot help much more than we have . Wix/Napa is perfect for his car. Good quality, right specs, priced right..easily found..but? Size which is fine for one model year later tha his is an issue? . Same with Mazda S2 RX8 filter that he inquired about. Helped with the research, found that it fits, although longer.Right spec;s he was concerned about. Found out pricing...Now seemingly only, wants something that hasn't been made in years. Oh well.


Its not that I want ONLY the filter discontinued by SOA years ago, but, I would prefer those if I could find a box.

So all this about the Wix "being too small" is only for the 06+ 2.5?
Posted by: ZeeOSix

Re: 23psi bpv oil filter for WRX? - 01/15/14 03:25 PM

Originally Posted By: 94exa2
I'm not hung up on the size. Same size as oem Subaru blue filter right?

I've read quite about about the Wix having a very small filter media, and not being able to flow enough for the Subaru oil pump.


If those two filters are about the same physical size, then how does their media surface area compare? Does the same physical sized OEM have that much more media?
Posted by: Eddie

Re: 23psi bpv oil filter for WRX? - 01/15/14 04:14 PM

Gads. Excellent options offered and declined. Nothing more to do here.
Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/15/14 06:59 PM

I appreciate the options given, but 99% of them don't have the 23psi bypass valve.
Posted by: ZeeOSix

Re: 23psi bpv oil filter for WRX? - 01/15/14 07:44 PM

Originally Posted By: 94exa2
I appreciate the options given, but 99% of them don't have the 23psi bypass valve.


Suggest contacting Purolator and ask them why they spec a filter for that car that doesn't have the higher bypass valve setting. I think everyone would like to here what Purolator says about that. whistle

http://www.purolatorautofilters.net/pages/ContactUs.aspx
Posted by: sxg6

Re: 23psi bpv oil filter for WRX? - 01/15/14 08:41 PM

Personally I use the oem blue subaru filter with my legacy.

I would use the 57712 wix/napa gold, but my knock on it would be it's flow rated at 9-11gpm. According to the factory service manual, the oil pump in my 2009 legacy is rated 1.2gpm @600rpm, 12.42gpm @5000rpm. The manual also says "or more" next to these values, so when my car is near red line at around 6300rpm, is my oil pump pushing around 15.64gpm?

The oem subaru oil filter is the only filter I trust to be designed with these specifications in mind, especially the high flow rating. Most aftermarket oil filter ive seen are rated at 8-11gpm or 9-11gpm.

Despite its more robust appearance, a member here said the old toyo roki filters bypass valve started to open at 18psi, not 23psi. He suspected that might be why subaru switched suppliers.
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1559859

I don't like that the rx8 filter goes into bypass later than the subaru filter, @26.1psi vs subaru 23.2psi. I'm ok with the bypass opening a little too early, but not with it opening late if the engine needs the extra oil flow.

Posted by: 94exa2

Re: 23psi bpv oil filter for WRX? - 01/17/14 08:53 AM

Originally Posted By: sxg6
Personally I use the oem blue subaru filter with my legacy.

I would use the 57712 wix/napa gold, but my knock on it would be it's flow rated at 9-11gpm. According to the factory service manual, the oil pump in my 2009 legacy is rated 1.2gpm @600rpm, 12.42gpm @5000rpm. The manual also says "or more" next to these values, so when my car is near red line at around 6300rpm, is my oil pump pushing around 15.64gpm?

The oem subaru oil filter is the only filter I trust to be designed with these specifications in mind, especially the high flow rating. Most aftermarket oil filter ive seen are rated at 8-11gpm or 9-11gpm.

Despite its more robust appearance, a member here said the old toyo roki filters bypass valve started to open at 18psi, not 23psi. He suspected that might be why subaru switched suppliers.
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1559859

I don't like that the rx8 filter goes into bypass later than the subaru filter, @26.1psi vs subaru 23.2psi. I'm ok with the bypass opening a little too early, but not with it opening late if the engine needs the extra oil flow.



My concerns exactly. Ive always read that most "aftermarket" oil filters dont flow enough for the Subaru oil pump, plus the lack of correct bypass valve.
Posted by: ZeeOSix

Re: 23psi bpv oil filter for WRX? - 01/17/14 11:18 AM

Originally Posted By: 94exa2
Ive always read that most "aftermarket" oil filters dont flow enough for the Subaru oil pump, plus the lack of correct bypass valve.


Where's the proof of that? Have you seen actual tests of flow vs. PSID for those filters, like the graph shown below? Or is it just some keyboard jockey's theory?

Based on this data from Purolator, this PureOne could flow enough for a Subaru oil pump. A 5 PSID at 12 GPM isn't really much pressure drop when you think about it.

http://www.bobistheoilguy.com/forums/ubb...451#Post1619451

Posted by: sxg6

Re: 23psi bpv oil filter for WRX? - 01/17/14 04:42 PM

When you pull up the specs for the wix 57712 oil filter, they state the following "Max Flow Rate: 9-11 GPM". I'll openly admit I don't know much about psid and pressure across the filter media. But what I do know is that they say that the max flow rate is 9-11gpm, and the subaru oil pump clearly exceeds that at times. So to the layman like myself, that concerns me.
Posted by: ZeeOSix

Re: 23psi bpv oil filter for WRX? - 01/17/14 04:57 PM

Originally Posted By: sxg6
When you pull up the specs for the wix 57712 oil filter, they state the following "Max Flow Rate: 9-11 GPM". I'll openly admit I don't know much about psid and pressure across the filter media. But what I do know is that they say that the max flow rate is 9-11gpm, and the subaru oil pump clearly exceeds that at times. So to the layman like myself, that concerns me.


Two questions:

1) Is this max oil flow volume specified by Subaru (as stated by 94exa2 above) the actual flow volume that goes through the filter & engine, or the gross flow volume the oil pump can put out with no resistance on the outlet of the pump? If it's the latter, it doesn't necessarily mean all of that flow goes through the filter & engine oiling system. Where is the spec/documentation that clearly states the oil flow that is actually going through the engine is 12~15 GPM as stated by 94exa2 above?

2) Is the WIX 57712 specified by WIX for the Subaru engine with such a high volume oil pump? If so, why did WIX specify that filter knowing the Subaru has such a high volume oiling system? WIX specified a higher 23 psi bypass valve, so they must know some performance details of the Subaru engine(s) they are specifying filters for.

Also, the "max flow" spec that WIX advertises means exactly what? The flow with X viscosity oil that results in the bypass valve opening? Or what ... ???

Sounds like a good question for someone to email WIX about to get some engineering input/clarification on what their "max flow" spec number really means.

What "max flow" spec would you tack on to the PureOne Flow vs PSID graph above? ... 18 ~ 20 GPM because that's about when the bypass valve would start to open? What I'm saying here is you have to fully understand what WIX's "max flow" spec really means to understand the real capability of the oil filter.
Posted by: ZeeOSix

Re: 23psi bpv oil filter for WRX? - 01/17/14 05:16 PM

Originally Posted By: sxg6

The oem subaru oil filter is the only filter I trust to be designed with these specifications in mind, especially the high flow rating. Most aftermarket oil filter ive seen are rated at 8-11gpm or 9-11gpm.


So have you actually seen any flow vs PSID data on the Subaru OEM oil filter? How do you really know it flows any better than say the WIX/NAPA Gold?

Keep in mind that these well known brand name aftermarket oil filter companies that specify one of their oil filters for these Subarus also claim that their oil filter meets OEM manufacturer's performance specs, and they warranty the filter to not cause any engine damage in their warranty claim statement.
Posted by: SHOZ

Re: 23psi bpv oil filter for WRX? - 01/17/14 07:13 PM

The Hyundai spin on filter has a 20 psi bypass.
Posted by: Izb

Re: 23psi bpv oil filter for WRX? - 01/18/14 12:01 AM

BEFORE any migration from original (Tokyo Roki) filter into Wix (57712 for EJ only, 57830 for FB only) the main question is:
What is filtration efficiency of original filter?
Posted by: Jim Allen

Re: 23psi bpv oil filter for WRX? - 01/18/14 08:14 AM

This question can be settled relatively easily.

Someone needs to install a DP gauge setup and measure DP with several filters. You could make a simple one by finding an adapter to go under the filter that has a port on each side of the filter oil flow (an aftermarket adapter for a cooler might work). Install a DP gauge or a single gauge on each side and read off the difference in pressures at various temps, loads and rpms. If the factory filter has significantly lower DP than the rest, you know it's a higher flow unit. If the others are equal, nearly equal or better, then you know "flow" is not an issue.

I think you guys are trying to fix a problem that doesn't exist. The filter manufacturers have access to data that we don't. Even it they don't physically test each part number of a vehicle, it logical to assume they check the data to make sure the part number meets the necessary specifications on paper at least.

Bypass pressure is as much based on the filter media as anything. A better flowing media (either via the amount of media or the type) might have a lower bypass setting. Sometimes the bypass setting is based on how much DP the media can accept. DP is also very dependent on the oil viscosity, as I have learned via the DP setup I have on my Ford 5.4L. With 30 grade oil, I was much closer to bypass, or bypassing more, than with the spec'ed 5W20 which basically never reaches bypass DP unless I rev to 5,000 rpm with the oil at 0F.

In any case, if someone wants to be a Subie Superhero and answer this question, it's a relatively simple process.