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post #1 of 17 Old October 28th, 2017, 02:07 AM Thread Starter
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journal bearing turbo oil question

hey, those of you running a high volume oil pump and a journal bearing turbo, what size restrictor are you running? cruising at 2500 rpm. my car makes lost 70 psi oil pressure, which is wayyy to high for a journal bearing to run without a restrictor.

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post #2 of 17 Old October 28th, 2017, 07:24 AM
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Are you leaking oil out of the seals? If not then you dont need a restickor. you don't use a resticktor on a journal bearing turbo unless it leaking out of seals, and you have ruled out the oil drain is not working properly.

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post #3 of 17 Old October 28th, 2017, 12:57 PM Thread Starter
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alright, turbonetics told me to run one if over 40-50 psi of pressure

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post #4 of 17 Old October 28th, 2017, 02:47 PM
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post #5 of 17 Old October 28th, 2017, 03:59 PM
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Here is some info from garrett
https://www.turbobygarrett.com/turbo...oil_restrictor

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post #6 of 17 Old October 28th, 2017, 06:23 PM
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What OP are you getting at idle? at WOT?


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post #7 of 17 Old October 29th, 2017, 12:35 AM Thread Starter
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Originally Posted by SSG Pate View Post
What OP are you getting at idle? at WOT?
hot idle 35-40, WOT 75ish

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post #8 of 17 Old October 29th, 2017, 12:36 PM
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Originally Posted by Snorky View Post
hot idle 35-40, WOT 75ish
You definately need a restricter then... my OP is a little higher at cruise and WOT and ill definitely be running one as well. The links posted are exactly what you need.

Less oil pressure coming in means less chance of over oiling and not being able to drain it out as well.


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post #9 of 17 Old October 29th, 2017, 01:21 PM
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How about lowering your oil pressure instead? Hot idle pressure of 35 psi is too high. What viscosity are you guys running? Do you monitor oil temps?

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post #10 of 17 Old October 29th, 2017, 06:22 PM
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This will take care of all the guess work. It will provide the 40psi of pressure at all times the turbos need. https://www.ebay.com/i/192225631113?chn=ps&dispItem=1

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post #11 of 17 Old October 29th, 2017, 06:44 PM Thread Starter
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damn! thanks for all of the help and knowledge guys!! I really appreciate the links as well. its crazy that a billet geared ford racing high volume oil pump will put out that kind of pressure.

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post #12 of 17 Old October 29th, 2017, 08:11 PM
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The pump doesn't put out pressure. It only sees flow. The pressure comes from the oil being restricted to flow through the block and parts. The higher the pressure, the more stress on the pump, and more power is lost trying to turn the pump against the higher pressure. A lot of people think higher pressure means better lubrication but that's not how it works. The pressure only insures the oil reaches the parts. It takes less than 10 psi at 1000 rpm to keep supply up throughout the engine. Most people aim for 20 psi at idle to extra safe. Power loss starts to occur at around 25 psi. Above 60 psi, the strain on the oil pump drive really starts to add up. At this pressure, the oil starts to heat up a lot from compression. The rule of 10 psi per 1000 rpm still rings true. The bypass for the oil pump should ideally open around 60-65 psi, which you shouldn't be getting close to until 5,000+ rpm. Once the oil reaches the bearing, rings, cams, etc... dynamic viscosity and pressure is no longer relevant as kinematic viscosity takes over. When the oil is dragged and spread through the bearing by the crankshaft's rotation, the oil doesn't see the pressure from the pump. It's now only affected by centrifugal forces and gravity. The pounding from combustion against the rod bearings determines shear action. Too much lubrication from too high of viscosity, while not as dangerous as too low of viscosity, can still cause excessive wear and localized overheating in the rotating assembly.

In the vast majority (95+%) of street engines, a high volume pump is not needed. The only time you really need a high volume pump is if you have wide bearing clearances with a lower viscosity oil with high a high flow rate through the bearings. The high pump is needed in those cases to keep up with demand. We're talking .0035" or greater clearances though.

I don't like the idea of a restrictor on the turbo feed. To me, that's just band-aiding the real problem of too high of oil pressure to begin with. The turbo doesn't need pressure, this is true, it needs flow. When you put in a restrictor to keep down pressure, you also decrease the flow. You're making a compromise that shouldn't have to be made.

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post #13 of 17 Old October 29th, 2017, 09:29 PM
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I do agree that his 35PSI idle pressure is high..... typically a MOD motor sees 20-25 PSI at hot idle. In order to build pressure you need flow and in order to flow a given amount of oil you need pressure to move the flow. But what is to much?? I personally have seen no research data to say what oil pressure is high enough to be counter productive.

As you can see i am around 25PSI at hot idle





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post #14 of 17 Old October 29th, 2017, 09:58 PM
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I saw such data at a tribology seminar I attended a couple years ago. In short, film strength and the base group of the oil are more important than the pressure. So long as the pressure is between 15-25 psi at hot idle and increases about 10 psi per 1000 rpm, you're fine. The only reason you want a little bit of pressure is because of the crankshaft. You want enough pressure to supply the crank and still have enough to supply the rod bearings as the centrifugal force of the crank throw will decrease the pressure as the oil makes its way to the bearings.

The graph for ideal lubrication looks like a V. At the bottom point of the V, you have ideal lubrication with sufficient pressure and viscosity at the desired temperature with good flow through the bearing to keep the bearing cool and little shear stress to stave off oil breakdown. At the left high end of the V, you have insufficient pressure/viscosity/ excessive temperature to maintain an oil film and metal to metal contact occurs. At the high right side of the V, you have too much pressure/viscosity/too little temperature that causes the oil to flow through the bearings too slowly causing a lot of shear stress and localized overheating in the bearings, plus power loss from the increased shear working against the crank.

This is why running the proper viscosity for your bearing clearances and engine oil temperature is important. Running excessive viscosity for the application puts you toward the upper right side of the V. Too low of viscosity puts you toward the left side of the V.

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post #15 of 17 Old November 3rd, 2017, 09:47 PM
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Quote:
Originally Posted by Snorky View Post
alright, turbonetics told me to run one if over 40-50 psi of pressure
This is some great insight that I was unaware of. I have a Turbonetics t62 non ball bearing Turbo and going to be running the MMR high volume oil pump with billet gears. Do I need a restricter as well?

I hope you figured out your issue with your oil pressure drop.
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post #16 of 17 Old November 3rd, 2017, 10:06 PM
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Originally Posted by RDY4WAR View Post
I saw such data at a tribology seminar I attended a couple years ago. In short, film strength and the base group of the oil are more important than the pressure. So long as the pressure is between 15-25 psi at hot idle and increases about 10 psi per 1000 rpm, you're fine. The only reason you want a little bit of pressure is because of the crankshaft. You want enough pressure to supply the crank and still have enough to supply the rod bearings as the centrifugal force of the crank throw will decrease the pressure as the oil makes its way to the bearings.

The graph for ideal lubrication looks like a V. At the bottom point of the V, you have ideal lubrication with sufficient pressure and viscosity at the desired temperature with good flow through the bearing to keep the bearing cool and little shear stress to stave off oil breakdown. At the left high end of the V, you have insufficient pressure/viscosity/ excessive temperature to maintain an oil film and metal to metal contact occurs. At the high right side of the V, you have too much pressure/viscosity/too little temperature that causes the oil to flow through the bearings too slowly causing a lot of shear stress and localized overheating in the bearings, plus power loss from the increased shear working against the crank.

This is why running the proper viscosity for your bearing clearances and engine oil temperature is important. Running excessive viscosity for the application puts you toward the upper right side of the V. Too low of viscosity puts you toward the left side of the V.

That may have something to do with why Ford changed from 5w30 to 5w20 since the bearing clearances were a little tight on the MOD motor.


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post #17 of 17 Old November 5th, 2017, 10:59 AM
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Quote:
Originally Posted by SSG Pate View Post
That may have something to do with why Ford changed from 5w30 to 5w20 since the bearing clearances were a little tight on the MOD motor.
That and aeration issues. The higher a fluid's viscosity, the more susceptible it is to trapping air pockets. (aeration) Think of honey or molasses with air pockets that hold in it compared to water where it rises right out. The same applies to engine oil. As oil gets churned through the engine, it gets aerated. If you could see inside an engine while it's running, you'd notice a film or foam on the surface of the oil in the pan. It's normal for that to happen, and it's not an issue with the proper viscosity as the air pockets will rise to the top and burn out. However, higher viscosity holds onto the air for much longer. In some cases, it can still be trapping air pockets in the oil as it gets sucked up into the oil pump. If aerated oil reaches a cam or crank bearing, you're going to have metal on metal contact. The MOD motors (and most any SOHC/DOHC engine with timing chains) are more susceptible to oil aeration due to the excess slosh from the chains and overhead valvetrain. The longer stroke and higher piston speed is responsible as well but not as much of an effect. What will spell instant death to a mod motor is if aerated oil reaches a chain tensioner and you lose the hydraulics holding the chain tight. This is the main reason the new Coyote comes with a 7qt oil capacity to help further combat this issue and help keep down the oil temps.

Which brings up the second point. OHC engines hold a lot more oil volume in the heads which means a lot more heat going into the oil. Lower viscosity oil can shed heat much easier than higher viscosity. It's the same principle as the aeration. With a demand on tighter tolerances, more efficiency, longer oil change intervals, and more reliability, the move to a 5w-20 made a lot of sense.

To keep this relevant to the OP, the addition of a journal bearing turbo will not change the viscosity requirement. The journal bearing works much like a cam or main bearing, just with a lot less load. So long as it has sufficient volume to it, it'll be fine.

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