Potential Cause of rumored GR86’s blown engine? Seal packing(RTV) was peeled off

[Tcoat]

Originally Posted by Spektyr

I could be wrong, but my understanding of fluid dynamics would say that there's a fairly small range of variation in diameter that would work. The inlet/outlet diameter of the oil pump itself is a big factor. At some point you have to funnel the pickup tube up/down to that size.

As your pickup tube diameter increases beyond the size of the oil pump inlet you're going to see less flow around the outside because the pump cannot lift the entire volume of oil in the tube uniformly. The height of the column of oil is set, so the wider you make the pickup the heavier that much oil becomes and the pump has only so much lifting power. The result will be a column of oil within the total volume that actually moves upward, concentrating any particulates or chunks suspended in the oil to that part of the screen.

As the center of the screen gets blocked, the column will "hunt" around for an unblocked path, kind of like a tornado looking for a trailer park.

Again, I'm not certain, but my guess would be that the smoothest, most efficient (laminar) flow would be achieved when the tip of the pickup tube is at or very close to the same surface area as the inlet of the oil pump, so I doubt that it's undersized.

In summery

[KillerBMotorsport]

Originally Posted by ROFL it's Waffle

Noob questions: I see the diameter of the pickup tube. How much oil is being sucked up at once? Is it a slow suction or fast? (not sure how to quantify this, maybe in cups per second or quarts per minute?)

At redline you're looking at ~2 gallons/min or 8 quarts/min. It's not a lot. The pump actually moves a LOT more than that when bench tested, but most of the oil goes out the bypass valve when on an engine.

[KillerBMotorsport]

Originally Posted by Grif

A close up and personal inspection of the oil pickup screen/basket.
Really gives you perspective of the surface area at play.

https://twitter.com/yonsama800/statu...69665373138945

Any chance you have some calipers and can measure the size of the open squares? Curious how close this is to the wire mesh used on past oil pickups.

[_____That_-_GUY_____]

Originally Posted by KillerBMotorsport

At redline you're looking at ~2 gallons/min or 8 quarts/min. It's not a lot. The pump actually moves a LOT more than that when bench tested, but most of the oil goes out the bypass valve when on an engine.

At 2 gallon/min, I can't see that there would be any issue with the oil cleanly finding a path through the screen, even if the top was completely blocked.

I feel like you could easily pour 2 gallons a min through a blocked tube, without a pump helping it along.

I wish a subura/toyota engineer would come out an say how the tube was tested.

[KillerBMotorsport]

Originally Posted by _____That_-_GUY_____

I feel like you could easily pour 2 gallons a min through a blocked tube, without a pump helping it along.

^ correct. 2 gal/min is not a lot.

[DocWalt]

If the pump is moving a LOT more than 2 gal/min at redline but bypassing much of it... that oil still needs to pass through the oil pickup tube.

The FA20DIT flows 15.9 GPM at redline, no clue if the FA24 is more or less.

and sucking through a restriction is a lot different than blowing through or even just free flowing through it.

[_____That_-_GUY_____]

I've worked on cars most of my life, but never to the level of building an engine. I wish there was an animation or video showing how the oil moves through a boxer engine. Curious to see how it flows.

[ROFL it's Waffle]

Originally Posted by KillerBMotorsport

At redline you're looking at ~2 gallons/min or 8 quarts/min. It's not a lot. The pump actually moves a LOT more than that when bench tested, but most of the oil goes out the bypass valve when on an engine.

Can the pump fail if it's running dry? (is the pump cooled by the oil)

[Tcoat]

Originally Posted by ROFL it's Waffle

Can the pump fail if it's running dry? (is the pump cooled by the oil)

It would have to run dry for a long long time(longer than the engine would run). It is a gear type pump that doesn't spin as fast as a rotary impeller or piston pump.
Not to say they can't fail but overheating them would be a pretty good achievement.

[KillerBMotorsport]

Originally Posted by DocWalt

The FA20DIT flows 15.9 GPM at redline, no clue if the FA24 is more or less.

That is the bench figure. No restrictions (like an engine), and no bypass flow.

[DocWalt]

Originally Posted by KillerBMotorsport

That is the bench figure. No restrictions (like an engine), and no bypass flow.

Again, bypass flow still has to go through the pickup.

also, positive displacement pumps always move the same amount of fluid given the same fluid conditions and RPM. They'll just generate more pressure (which gets relieved out the bypass when not needed)

[Ultramaroon]

Originally Posted by KillerBMotorsport

At redline you're looking at ~2 gallons/min or 8 quarts/min. It's not a lot. The pump actually moves a LOT more than that when bench tested, but most of the oil goes out the bypass valve when on an engine.

Originally Posted by KillerBMotorsport

That is the bench figure. No restrictions (like an engine), and no bypass flow.

I don't think the fa20 has a regulator, There's only the relief valve which I understand opens at 140-ish PSI. If it had a regulator, pressure would not fluctuate dramatically with RPM and temp. It would also not hit 120 PSI at high idle on cold start.


It's PD all the way.

[KillerBMotorsport]

Originally Posted by _____That_-_GUY_____

Curious to see how it flows.

From sump, to pump, filter, LH head, block, to RH head. This is the path and order across the main galleys.

Originally Posted by DocWalt

Again, bypass flow still has to go through the pickup.

No. Bypassed oil goes right back into the suction side of the pump. It's all contained within the pump.

Originally Posted by DocWalt

also, positive displacement pumps always move the same amount of fluid given the same fluid conditions and RPM. They'll just generate more pressure (which gets relieved out the bypass when not needed)

That would be true if it weren't dynamic, but the pump is constantly changing RPM. Not only that, but the system's flow rate also is changing due to temperature and AVCS demand.

Originally Posted by Ultramaroon

I don't think the fa20 has a regulator, There's only the relief valve which I understand opens at 140-ish PSI. If it had a regulator, pressure would not fluctuate dramatically with RPM and temp. It would also not hit 120 PSI at high idle on cold start.

Some call it a regulator, some call it a bypass. It's the same thing.

It does not open at 140psi.

Here's a plot showing oil pressure. Where the ramp rates change is where the bypass just cracks open and starts regulating. I would call it 75psi... which coincidentally, it right in line with 95% of the other oil pumps Subaru uses. The reason pressure keeps climbing after the bypass opens is because flow is increasing, further compressing the bypass spring, requiring more pressure to keep it open enough for the additional flow. Eventually what can happen is the bypass will aerate (if you have too big of a pump and an engine not made for it, for example), because flow out the bypass is horribly turbulent. Think of water coming out of a hose with your thumb covering the end. If you run too big of a pump AND shim it to increase pressure, then that inner gerotor usually lives a short and violent life.

Flow is linear with RPM through the rotors (assuming constant temp and no AVCS). The bypass valve regulates the pressure and flow actually going into the engine.

[KillerBMotorsport]

I don't have any comparative oil pump data for the FA24 yet, but here's one from an EJ (2019 STi) showing a 10mm, 11mm, and 12mm pump on the same engine.




And here's a No-Load plot showing the point that the bypass valve starts regulating oil pressure...