Beating the horse to death: Subaru and Fram Ultras

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So here's something for all you non-believers in the higher bypass pressure, and what you also need to consider. In another thread, several years ago, ZeeOSix posted a delta-P chart that showed 12gpm@200*F is 5 psid. Now, I'm no mechanical engineer, but when ALL of the available oil filters spec max flow rates at 8-10GPM, and we are dealing with an oil pump that we KNOW flows at least 12GPM at 5K rpm, and has another 1500RPM to go to redline, riddle me this: What, pray tell, happens to delta-P as the oil flow rate of the oil pump starts to exceed the flow rate of the filter and media?? Sure sounds like a prime candidate for delta-P to spike!

If flow is 1GPM@600RPM, and nearly 12GPM@5000RPM, we can extrapolate that the flow at 6,500RPM is >15 GPM, which far exceeds the flow ratings of these filters (Fram doesn't seem to publish max GPM ratings of its filters/media?). This is at a minimum 50% and possibly 90% higher than the rating of the Wix filters (even the XP) so pray tell, do you still think an 8-11psi bypass is going to stay shut when exposed to these conditions? Even if the oil is hot, ZeeOSix's PSID chart shows the filter will be at a minimum, 7.5PSID across the media. I'm not going to trust my engine to likely less than 0.5# of spring pressure between it and unfiltered oil. Just sayin'.
 
The deta-p doesn't "spike", but will have a curve shaped similar to the PureOne curve. Most filters will have a bypass valve set to at least 12 PSI, typically a bit more. So with hot oil it would still be hard to hit bypass, even at 12 GPM of flow from the pump.

Could be that Subaru doesn't like their filters to bypass on cold start-ups assuming that their cars might get high revs before the oil is fully hot.

Another thing that happens with cold thick oil at high engine revs is the oil pump will hit pressure relief, which will cut back the oil flow volume going to the filter and engine. That also helps limit delta-p across the filter.
 
Originally Posted By: SubieRubyRoo
So here's something for all you non-believers in the higher bypass pressure, and what you also need to consider. In another thread, several years ago, ZeeOSix posted a delta-P chart that showed 12gpm@200*F is 5 psid. Now, I'm no mechanical engineer, but when ALL of the available oil filters spec max flow rates at 8-10GPM, and we are dealing with an oil pump that we KNOW flows at least 12GPM at 5K rpm, and has another 1500RPM to go to redline, riddle me this: What, pray tell, happens to delta-P as the oil flow rate of the oil pump starts to exceed the flow rate of the filter and media?? Sure sounds like a prime candidate for delta-P to spike!

If flow is 1GPM@600RPM, and nearly 12GPM@5000RPM, we can extrapolate that the flow at 6,500RPM is >15 GPM, which far exceeds the flow ratings of these filters (Fram doesn't seem to publish max GPM ratings of its filters/media?). This is at a minimum 50% and possibly 90% higher than the rating of the Wix filters (even the XP) so pray tell, do you still think an 8-11psi bypass is going to stay shut when exposed to these conditions? Even if the oil is hot, ZeeOSix's PSID chart shows the filter will be at a minimum, 7.5PSID across the media. I'm not going to trust my engine to likely less than 0.5# of spring pressure between it and unfiltered oil. Just sayin'.


I understand what you're saying, but the bypass pressure is RELATIVE, based on the flow restriction of the media. So a media that has less restriction (FU) will not generate an equivalent psi of flow restriction as compared to a cellulose media filter until a higher flow rate. And, according to the tech at Fram with whom I spoke via phone, they are very confident that they meet or exceed the Subaru OEM spec for the actual amount of oil that actually gets bypassed and how often this occurs.

So, at 12gpm, a syn media filter such as the FU may only generate 6-9psi of pressure differential across the media, whereas cellulose may generate something on the order of 14-22psi, assuming similar beta ratios. So, the "bypass pressure rating" isn't always the "bypass pressure rating".
 
All well and good points, but why does Fram use cellulose blend for their racing filters and not the Ultra? They have a 22 psi bypass, and a larger bypass according to them. I have asked this before.
 
Originally Posted By: goodtimes
All well and good points, but why does Fram use cellulose blend for their racing filters and not the Ultra? They have a 22 psi bypass, and a larger bypass according to them. I have asked this before.

Flow > filtration for the Racing series, and also a heavier can to keep the NHRA and SFI happy.
 
Turns out the owner of said Subaru called me and asked me if the oil change special at O'Reilly was good enough - and it was. She got the proper Subaru-spec Wix and 5 quarts of Mobil Super 0-20.

I'll find something else to install those XG7317s on.
smile.gif
 
Originally Posted By: SubieRubyRoo
Please, do tell, why would they specify 24/27 psi bypass if it wasn't necessary?


I'm not sure why they spec that high - but I'm saying the filter might see those conditions .0000001% of the time the car is in service life.... and with a filter that should have been changed a LONG time ago!

Yes, there are some lead foot drivers that will spike it when cold, but that's just not the "norm".

99.9999999% of the time, the filter media just is not that restrictive - well, not 27 PSID restrictive, anyway.

To see 26.99 PSID (LOL, just under 27 PSID bypass pressure) is an event that most certainly must be very, very rare indeed. Even if it does occur, the instance will be VERY BRIEF.

I made my comment b4cause the better synthetic media can be used even with a 12 PSID bypass, because the media flows more easily and the bypass condition will be just as UNLIKELY to be achieved as the 27 PSID setting in a paper filter.
 
Originally Posted By: BufordTJustice
I understand what you're saying, but the bypass pressure is RELATIVE, based on the flow restriction of the media. So a media that has less restriction (FU) will not generate an equivalent psi of flow restriction as compared to a cellulose media filter until a higher flow rate.

So, at 12gpm, a syn media filter such as the FU may only generate 6-9psi of pressure differential across the media, whereas cellulose may generate something on the order of 14-22psi, assuming similar beta ratios. So, the "bypass pressure rating" isn't always the "bypass pressure rating".


^^ Yes, this makes perfect sense. ^^

I have watched enough filter flow test videos in my life now to fully believe a filter's media flows a lot more than we like to give it credit for.

Bypass valve PSID ratings be dmnned......
that event just does NOT happen all that often,
and on some engines - if ever.
 
Interesting data on the Subaru oil pump. That seems like a very large oil pump, about 3 inch diameter, compared to what I remember on much larger American engines of old. The width is probably narrower though.
It is often said on here oil pump is positive displacement, flow the same, yet here we see they specify a flow rate at 176 deg, hot oil. What is the explanation?
 
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Originally Posted By: Linctex
I have watched enough filter flow test videos in my life now to fully believe a filter's media flows a lot more than we like to give it credit for.


Flow test videos? Did they show delta-p vs flow measurements and resulting data? Got links?
 
Originally Posted By: goodtimes
It is often said on here oil pump is positive displacement, flow the same, yet here we see they specify a flow rate at 176 deg, hot oil. What is the explanation?


Don't know why they chose 176 F for the pump flow spec. It's possible the pump will lose a little performance at hotter oil temps (thinner oil) due to pump "slip", but it won't be much if the pump has tight clearances.
 
so the takeaway from all this is that the 3.6R engine in late model Outbacks need either the OEM Subaru filter or a Wix XP/Napa model? If not the OEM what model for the Wix XP?
 
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