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journal bearing turbo oil question

5K views 16 replies 6 participants last post by  RDY4WAR 
#1 ·
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.
 
#2 ·
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.
 
#15 ·
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.
 
#6 ·
What OP are you getting at idle? at WOT?
 
#11 ·
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.
 
#12 ·
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.
 
#13 ·
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



 
#14 ·
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.
 
#16 ·
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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