GEROTOR pump, dry sump engine pressure problem 1

[fabiom75]

We have built a race engine. It's a 2jz-gte supra 3 liters engine and we have applied a dry sump kit.
We are actually using a peterson gerotor 3 stages pump rated at 18/20gpm (at how many rpms?)
We have a 5 gal tank in the trunk and a -16an line going to the pump and -12an line pumping oil inside the engine.
2 scavenging lines keeps the tank always at at least 2/3 of the level.

Here is the problem:
hot oil, idle 1600rpms, 28psi of oil pressure.
everything is ok so far.
Increasing the engine rpms we see an incease in flow and pressure. We are actually using evne a flow meter gauge.
Everything is ok up to about 6k rpms engine speed where we have about 117psi of pressure and 16gpm of oil flow.
At this point we have problems:
keeping the engine STEADY at 6k rpms we start to see a drop of oil pressure BUT NOT a drop in flow and this could be caused MAYBE by the increasing of oil temperature and loss of oil viscosity.
If we increase the engine rpms we have an even more accentuated loss of oil pressure but still absolutely no loss of oil flow.

The actual pump ratio is 52% so cavitation due to excessive pump speed should be possible. These pumps are rated at well more then 5k pump rpms. At 6k engine rpms we are at about 3k pump rpms.

Cavitation due to small inlet line should not be the case as well. We are using the -16an line as per pump instructions. The oil line have no tight bents.

The actual gerotor is 1.1 inches wide. The stock oil pump is 0.8inches BUT spinning at 100% of engine speed.
The external of the actual pump is about 2.75inches. While the stock pump was 4.3inches.

Could be the actual pump undersized?
Is there any way to calculate the oil volume that the stock pump was flowing based on the rpms/gerotor size?

Any help would me really appreciated.

 

[kenre]

Possibly the relief valve is opening reducing pressure.

 

[Fabrico]

Do you have an oil cooler?

Where is the relief valve? Does it flow enough? Is it working properly?

 

[fabiom75]

We have been thinking about the relief valve but it is working properly: the valve is inisde the pump. We have removed it and inspected but it looks ok. we even tried to use teh pump with the valve completely forced to remain closed (we removed teh spring and replace wit with a bar) but still the same exact problem.

We use an oil cooler yes and it is way over rated with 2 inlets and 2 outlets -12an each of them.

 

[qwester]

Here's a thought. Engine is hot. Most bearing clearances expand with temperature. Oil viscosity decreases with temperature, pressure drops. Geroter pump depends on mass transfer not friction so it is not as sensitive to temperature. Oil density does not decrease as much as viscosity with temperature so it will move oil at a more or less constant rate. I do not believe you have a problem.

Engine oil pump is more likely to have loss of pressure with temperature due to leakage and turbulence as well as increased bearing clearances.

 

[fabiom75]

qwester, we have been thinking about that indeed. About the fact that we could not have a real problem. But, why at 4k engine rpms we have absolutely no oil pressure drop while we have at 6krpms? Maybe as at 4k engine rpms the oil pressure is way over the relief valve point?
We have set the relief valve point at 117psi.
The problem is that the engine have a red line of 10500rpms and at 7krpm we alreayd have an huge oil pressure drop. At 7k rpms teh oil pressure is already at 70psi and lowering quickly. At 8krpms we read 58psi of oil pressure that is WAY too low.

The stock oil pump was able to keep a linear oil presusre up to the red line.

Maybe we need to go to 1:1 speed ratio?

 

[MikeHalloran]

It appears that you need a wider gerotor.

Before you risk engine damage, set up a bench test. Drive the original oil pump and the gerotor pump in turn with an electric motor, pumping oil to and from a bucket. Measure the flow of each, and compute the flow per pump revolution.



Mike Halloran
Pembroke Pines, FL, USA

 

[SMOKEY44211]

The reason why you are seeing a drop in pressure is air is being churned into the oil. A lot of people conclude that it is the result of higher oil temps. which coincidently rises at about the same rate that air gets entrapped into the oil. To prove it out preheat the oil after it has been setting for 4 or more hours ( giving the air time to escape). Pressure #'s will be back up until it gets airated again.--------Phil

 

[fabiom75]

Smokey if that is the case how to fix it?

 

[Milanoguy]

Fabiom75

What kind of oil are you using? I recall in another forum, a similar problem, the problem went away when they changed to a non detergent synthetic oil. Apparently a lot of modern synthetic oils, especially the ones that advertise a long duration between oil changes have too much detergent in them.

When the oil is being thrashed about at high speed(read high RPM) the detergent turns into froth which is why the oil presure goes down.

If you have a breather valve in either the head or the block try and connect a clear plastic hose to the breather. Then run the engine. If the clear hose fills with froth you have a problem. Try running non detergent oil and see if that helps.

Bye for now

 

[patprimmer]

To decrease aeration, ensure oil scraper is efficient, oil drain back areas keep oil away from rotating parts.

Make sure oil tank has scavenge lines arranged so the returned oil is striking the inside of the curve of a curved surface. It should strike at a tangent well above the oil level and above a screen that will "filter out: air bubbles.

Some if not all oils contain anti foaming agents. An oil with a good anti foam package should help.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[fabiom75]

Milanoguy,

I am using the MOTUL 300V competition oil.Not sure about the level of detergent inside it.
I have an hole in the head where originally were palced the hose for the oil vapours. I will use that place to do the test. But I don't think that even if the oil is foaming it will be so bad that it will arrive up there and fill the hose.

Patprimmer sincerely I'm not so sure about areation. I really don' tthink that our problem is that.
I use a moroso tank that should perform very well and divide oil and air very efficently...

I still think about a volume problem compared to the stock pump.

 

[patprimmer]

My experience is that to small a pump drops pressure across the board.

A drop off at high speed is normally the level in the sump dropping and uncovering the pickup (unlikely with a half decent dry sump) or the pickup sucking up the bottom of the sump (impossible on a dry sump unless the sump fabricator/designer was a complete idiot).

The other possibility is that the bearing and journal acts as an eccentric pump and centrifugal force pulls oil from the main gallery. These could combine to decrease the rate of pressure build up with speed. Porsche used very small oil holes in their cranks many years ago to reduce that tendency.

Is there any sign of the bearings being overheated. 117 psi at 6000 rpm sounds like plenty of pressure to me, and as the flow is good, presuming the oil quality (read contains little or no air) I don't see a problem.

The only function of pressure is to induce sufficient flow to ALL points required, hence the small crank drilling so as to leave sufficient pressure in the main gallery to stop the big ends robbing to much from the mains. The only anomaly I see with this explanation is the pressure should taper off rather than hit a wall or actually decrease.

A very simple test would be to try another oil.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[SMOKEY44211]

I think any strategy that gets the oil away from the crank will reduce the airation. As Pat mentioned a scaper that is installed tangent to the counter wieghts goes a long way to achieving that task. I have seen a # of commercially available scrapers that install perpendicular to the crank. My experience with them is they actually agrivate the problem. In your aplication have you isolated or can you isolate the oil from the top end from potentially draining back over the crank?---------Phil

 

[fabiom75]

I have an update: we have tested the engine at 8krpms.
We have even more flow ( 20gpm ) but even less oil pressure (about 60psi of oil pressure...)
So the flow increases but the oil pressure go down and down...
At this point is it a problem of a too small oil pump?

 

[WilliamH]

I think Pat and Smokey are on the cause---air ingestion. If you can look into the oil tank and see a vortex forming as engine speed increases you may have a direct air source to the pump inlet. This is very common on poorly designed dry sump oil reservoirs. This is like watching the coriolis effect when a bathtub drains.

Additionally, in my opinion, the dry sump pressure section is too large or your relief valve is adjusted too high. A good correlation is 10 psi per 1000 rpm. Also, I am assuming that the relieved oil feeds back to the inlet of the pressure stage.

Another possible scenario is a restricted or collapsing oil suction hose to the pump inlet.

 

[GregLocock]

Another option is that you have reached the centrifugal limit of the oil ways and bearings.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[fabiom75]

GregLocock,

what do you mean? can you explain?



Thanks

 

[GregLocock]

Post 9 in this thread

http://forums.autosport.com/showthread.php?s=&threadid=90890

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[SMOKEY44211]

Given the latest info that you posted there is a possibility that you are hemorrageing the oil somewhere. I'm not that familier with the engine in question. If the block and/or head(s) are of aluminum material the internal clearances would increase with rise in temp. more so then a cast iron counterpart. This is assuming an overhead cam with pressure fed cam bearings. Its impossible to get the clearances "right" for a wide range of operating temperatures with a bearing that is clamped into an aluminum housing. If your engine fits any of the criteria you may have to step up the pump sizing or decrease the internal clearances and use a method of preheating the engine.---------Phil