Alternate Dry Sump Design?

[Hobby Racer]

My 818R build uses an EZ36 flat 6 Subaru engine, so there are no off the self dry sump solutions to be had. My main concern is maintaining oil pressure while on track. As I am running the motor naturally aspirated, there is little benefit to creating a vacuum in the crankcase like there would be if running boost. Also the OEM pan is already only about 2 inches deep so there would be no height reduction by running a typical dry sump pan. This got me thinking, is it possible to run a dry sump system differently than the usual setup used in Subaru motors?

Typical Subaru setups run two or more scavenge stages and use the OEM pump instead of an external pressure stage. Oil moves through the system as follows:

1. Custom dry sump pan
2. External pump with multiple scavenge stages
3. Dry sump tank
4. OEM pump
5. External filter & cooler
6. Engine block

I was thinking of using the OEM pump as the scavenge system and then using an external pressure stage to feed the motor. The system would run in the following order:

1. OEM oil pan
2. OEM pump
3. External Filter & Cooler
4. Dry Sump Tank
5. External Pressure Stage
6. Engine block

This has some nice advantages. Fewer components, only a single pressure stage to drive off the crank, and less to modify on the engine. It uses the stock oil pan and fewer external lines. The oil is filtered and cooled before it enters the dry sump tank. I'm trying to think of any down sides to this idea, let me know what you think.

[EODTech87]

Biggest issue I can think of is that if your OEM pump is running at very low pressure(say at idle) and your external pressure was pushing to much oil into the engine you would fill the engine with oil. You would have to ensure your OEM pump is always flowing more than your external pressure stage which could be difficult.

[Hobby Racer]

I think it will be ok. The OEM pump should flow quite a bit since it will only be forcing oil through the filter and cooler and not the entire engine. So while the pressure might not be high at idle, the volume should be high.

At least that is how I'm thinking about it

Your right though, the OEM pump must discharge a higher volume than the external pressure pump at all times for this to work correctly. How to test that?

[DanielsDM]

I think it will be ok. The OEM pump should flow quite a bit since it will only be forcing oil through the filter and cooler and not the entire engine. So while the pressure might not be high at idle, the volume should be high.

At least that is how I'm thinking about it

Gear pumps are positive displacement pumps so the volume it moves is independent of the pressure (caused by the downstream restriction). Volume will be directly proportional to rpm and reducing the downstream restriction (by going to the DS tank instead of through the block journals and ports) won't increase the volumetric flow. I don't think the OEM pump can move enough volume to scavenge properly and you will basically have a system that works like a wet sump with a 12qt accusump.

Not saying in won't work, the following scenario seems plausible:
In a high g corner the oil returned to the pan doesn't make it to the pickup, OEM pump sucks air, the external pressure pump pulls from the tank, after the corner the OEM pump starts pumping oil again and refills the tank. If the tank is large enough the pressure pump is never starved. With a 12qt tank and a pump that flows 50 qts/min you get about 15 seconds before it's empty. Then if the OEM pump also flows 50 qt/min you need 15 seconds of straight to refill it.

[Hobby Racer]

With a 12qt tank and a pump that flows 50 qts/min you get about 15 seconds before it's empty. Then if the OEM pump also flows 50 qt/min you need 15 seconds of straight to refill it.

If the pressure pump and OEM pump both flow 50 qt/min the system would not work. The OEM pump would never be able to evacuate the pan. Any oil accumulated in the pan due to the OEM pump sucking air in a high G corner would stay as the external pump is constantly pumping in the same volume as the OEM is pumping out.

For this to work the OEM pump MUST pump more volume than the external pump. If the OEM pump recirculates excess oil volume internally via the pressure relief spring under normal operating conditions, then under my setup that extra oil volume would be pushed to the dry sump tank. That paired with a properly downsized external pressure pump should make this system work reliably.

Is my logic correct?

[NAZ]

I studied hydraulic engineering when I was in college and later as an engineer, I designed a few systems and modified several others. However, hydraulic engineering is not my speciality. I have never designed or modified an automotive dry sump system but the basics of these systems are similar enough to other hydraulic systems I have worked with that I can weigh-in and at least give you something to ponder.

There's a reason you see dry sump pumps all as a unit. You size the pumps to the needs of the system and in relation to each other so that you get an adequate supply volume and scavenge pumps sized to ensure the pan is evacuated. You also need to design the supply tank to match the flow volume of the supply pump and there is a minimum size that must be calculated not guessed at. As stated above, these positive displacement pumps will create more flow as the speed increases and since they are all connected their speed is ramped up and down together. The flow differential remains constant -- as the speed increases (and flow increases) on one pump it also increases proportionally on the other pump(s). If you are trying to run a split system you will end up with a Rube Goldberg control system as you have to control the flow of the supply pump proportionally to the flow of the OEM oil pump you are now using as a scavenge pump. A very difficult task (and expensive) that will be much more complicated than a conventional dry sump system where the external pumps are driven off the crank by a belt. There is nothing to control on a conventional system (except a pressure relief circuit which is required on any positive displacement pump). A conventional dry sump pumping system is simple and robust.

So, can someone design a dry sump system that uses an OEM oil pump as the scavenge pump? Yes, a sharp engineer with relevant experience could but is it an improvement over a conventional dry sump system? Would it be easier to adapt a conventional dry sump system to your engine?

[DanielsDM]

If the pressure pump and OEM pump both flow 50 qt/min the system would not work...

...Is my logic correct?

Yes. This is why DS setups use 2 or more stage scavenge pumps. The scavenge pump has to flow a lot more to "catch up". Without real data on the flow requirements of the engine and the OEM pump it's hard to say if it would work or not. Maybe if the oversized OEM gears are used (11mm or 12mm thick)?
I wouldn't go down this road without actual test data on the flowrates. A engine rebuild is an expensive way to find out it didn't work.

I'm using a 4 stage external pump (3 scavenge, 1 pressure) and eliminating the OEM pump.

[CdnCarNut]

You could always try the empirical, scientific approach. Try a few different sizes of scavenge pumps and plot how long the engine lasts vs. the volume flow of the pump. After 3 or 4 engines/rebuilds, you will zero in on the optimal scavenge pump! ;-)

[Sgt.Gator]

Hobby, Interesting idea. I've been trying to figure out how to dry sump an EZ30/EZ36 and hadn't come up with this solution. And it also has to work in the confined space of an 818, unlike the room in front of a WRX/STI/Legacy.

Here's part of the info you need. These are EJ series pumps though, I don't know where to find EZ series. I'll look around for that. But these should give you an idea.



H6 Oil Pump from FSM



H6 Oil Flow:



More H6 Notes:



And on the EZ36 there is a low oil level sensor which might cause problems with your idea in it:

[DodgyTim]

The oil in the sump is likely to be frothy in high g corners due to high engine revs, with very little time to defroth, so the oem pump would pump less mass. In a normal engine the densest oil ( with the least Air) is picked up. With the system you describe using the oem pump as scavenge, the oem pump would be trying to pump much more aerated oil.
The oil in the dry sump tank should be largely defrothed, due to longer time and swirling feed, so there is an inherent unbalance in the systems
That's another reason the scavenge systems flow much more volume than the delivery systems, and also makes calculating the pump sizes very difficult

[Hobby Racer]

And it also has to work in the confined space of an 818, unlike the room in front of a WRX/STI/Legacy.

That is one of the big issues I'm dealing with. There is not enough room to run the typical dry sump mandrel pulley off the crank. You must run a single serpentine belt system for it to fit.

And on the EZ36 there is a low oil level sensor which might cause problems with your idea in it:

I removed that sensor, so no issue there.

[Hobby Racer]

Lots of good feed back here. Most likely not a viable solution but I like to think outside the box. Sometimes you come up with a winner.

[EODTech87]

If there are a few people interested in a EZ36 dry sump you might be able to work with someone who could machine a dry sump pan. DanielsDM machined his own pan(EJ series) so you might contact him.

http://thefactoryfiveforum.com/showt...l=1#post288518

[Zach34]

Machining services are more accessible now than ever. Most of your challenge with a custom system will be a good CAD design for the pan and pump bracketry. Might be easier than the trial/error process of transforming the oem pump into a scavenge stage

[Sgt.Gator]

Hobby do you follow this thread on NASIOC? "The H6 Impreza Resource Thread". https://forums.nasioc.com/forums/sho....php?t=1323800

I see that Jeff Sponaugle is posting in there. As you may recall he bought an 818 kit and was a frequent poster on this board a few years ago. I don't know why he hasn't posted here in so long, he is a great resource for all things Subaru and especially because he has the two 500HP+ H6 builds that he and Jeff Perrin built years ago. Jeff now has both cars. He mentions losing oil pressure the last time at the track in hard turns... https://forums.nasioc.com/forums/sho...postcount=3434

I wish he'd get his 818 project going again and get back to posting here.

And if you want to read Perrin's build blog: https://www.perrin.com/blog/post/perrin-h6-build-up

[lance corsi]

Engine tilts the wrong way. You will need to correct this if you want a proper oil system to work correctly. Most don't want to admit or correct this. It takes some work.

[Hobby Racer]

Engine tilts the wrong way. You will need to correct this if you want a proper oil system to work correctly. Most don't want to admit or correct this. It takes some work.

Already fixed that. Raised the front motor mounts and lowered the rear trans mount
I originally did this to make the EZ36 fit better (clearance to the front fire wall) but it has turned out to have other benefits as well!

After.jpg

[Hobby Racer]

Hobby do you follow this thread on NASIOC? "The H6 Impreza Resource Thread". https://forums.nasioc.com/forums/sho....php?t=1323800

I see that Jeff Sponaugle is posting in there. As you may recall he bought an 818 kit and was a frequent poster on this board a few years ago. I don't know why he hasn't posted here in so long, he is a great resource for all things Subaru and especially because he has the two 500HP+ H6 builds that he and Jeff Perrin built years ago. Jeff now has both cars. He mentions losing oil pressure the last time at the track in hard turns... https://forums.nasioc.com/forums/sho...postcount=3434

I wish he'd get his 818 project going again and get back to posting here.

And if you want to read Perrin's build blog: https://www.perrin.com/blog/post/perrin-h6-build-up

Yes I have read all those threads, some great stuff, but no dry sump info.

[Wayne Presley]

Hobby do you follow this thread on NASIOC? "The H6 Impreza Resource Thread". https://forums.nasioc.com/forums/sho....php?t=1323800

I see that Jeff Sponaugle is posting in there. As you may recall he bought an 818 kit and was a frequent poster on this board a few years ago. I don't know why he hasn't posted here in so long, he is a great resource for all things Subaru and especially because he has the two 500HP+ H6 builds that he and Jeff Perrin built years ago.

Well Jeff put new turbos on his GTO and getting his 1000 HP GTR back on the road...He may be busy...