oil pressure

[nm9stheham]

And YES, shimming the oil pump spring DID help my hot , low oil pressure !

So big block? Been 38 years since I touched one LOL. But with the pump at the front of the block and if the measurement pickup is at the rear, that probably explains the low hot idle pressure.... it is at the far end of the system, after all the other pressure drops. How cool is the engine at these cold startups FB ? OK can be pretty cold in some parts during the winter.

I still can't quite see how shimming the relief valve helped it unless the relief valve is always open to some degree.... which I suppose is possible with the very high cold pressure.

 

[AndyF]

this ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I have the hi volume pump spring shimmed to get the hot / idle pressure to what it is, thus the hi cold start up pressure.
ONLY run mopar filters, and have had to tighten them a hair more than normal on install. , just forgot to this time.
I used to run Phillups troparctic 20w40 in my new 68 barracuda back in the day, but haven`t seen any for yrs., would not be vmuch diff. than 20w50 I just took out , because of colder weather!

I think the problem is that you shimmed the spring. That is why you have such high cold pressure. Take the shim out and/or put in a soft spring and then shim the soft spring to get you the correct pressure at speed. Typically with a high volume pump you need to run a shimmed soft spring to get the correct balance between oil pressure at idle and at full throttle.

 

[Mattax]

any body got any idea how to drop upper and cold start oil pressure , "with out" , dropping the hot idle pressure

Yes. Use an oil with same hot viscosity as now, but that has a lower cold temperature viscosity.

I'm saying take whatever grade oil you have now (10w40) and raise the cold (first) number

Don't you mean the other way around? Say like a 5w40? That would lower the oil pressure when cold and keep the same when hot?

You might be right...but shouldn't the higher number flow better then the low number ?
Warm oil flows better then cold oil, doesn't it?

Yes Warm oil flows better than cold. The only thing you had backward is how the SAE numbers work.
The higher the number, the thicker the oil.
One way to think of a multi-grade oil is like this example. A 20W-50 has viscosity more like a 20 'weight' at cold temperatures, and the same as a 50 'weight' at hot temperatures. Technically this is not exactly correct, but its basically right.

Here's a visual comparison of the viscosity of Brad Penn's straight 40 oil and some multi-grade 40s.
Look at the viscosity of each at 68*F.

At 68 F, the viscosity of the straight 40 is around 500 centi-Stokes.
While the viscosity of the 15W-40 oils are around 350 centi-stokes.
and the Rotella T6 5W-40 is only about 225 centi-Stoke.

Once they are up to 212 * F, they all must be between 12.5 to 16.3 cSt. In this example all are 15.5 cSt except for the 5W-40.

 

[Mattax]

I think the problem is that you shimmed the spring. That is why you have such high cold pressure. Take the shim out and/or put in a soft spring and then shim the soft spring to get you the correct pressure at speed. Typically with a high volume pump you need to run a shimmed soft spring to get the correct balance between oil pressure at idle and at full throttle.

Andy, Where do you typically read oil pressure when working on your big blocks?

 

[AndyF]

Andy, Where do you typically read oil pressure when working on your big blocks?

View attachment 1715264546

I've found that it doesn't matter where you read the oil pressure. The reading will be the same at either end of the engine. I once hooked up three oil pressure gauges to a big block just to check it for myself. One was at the outlet of the pump, one was at the inlet to the block and the third was at the back of the block. All three read the same so I got rid of two of the gauges.

 

[famous bob]

I've found that it doesn't matter where you read the oil pressure. The reading will be the same at either end of the engine. I once hooked up three oil pressure gauges to a big block just to check it for myself. One was at the outlet of the pump, one was at the inlet to the block and the third was at the back of the block. All three read the same so I got rid of two of the gauges.

Andy; wouldn`t the oil pressure relief valve opening sooner drop the oil pressure straight across the rpm range , because it would open
quicker ? I might have mis-stated the restricted oil t o the top end. I have full time oiling to the top, and had to restrict it the best I could w/o pulling the heads.
I made the mistake of drilling the lifter galley deal like a guy on here said he did all his engines, it put way too much oil up there, ( big mistake guys, don't do that ) , so I restricted the drilled holes the best I could /under the intake. Then tied the tubes going up , together w/ 1/16'' line, and machined a couple of restrictors to go around the bolts that feed the rockers, therefor closing the opening around the bolts down.
I suspect I still may have a little too much to the top, AND , can drill and install jet type restrictors in the deck surface, if I ever have to pull the heads, which I really don't want to do if I don't have to.
THANKS , for all comments -------------------------

 

[Mattax]

I've found that it doesn't matter where you read the oil pressure. The reading will be the same at either end of the engine. I once hooked up three oil pressure gauges to a big block just to check it for myself. One was at the outlet of the pump, one was at the inlet to the block and the third was at the back of the block. All three read the same so I got rid of two of the gauges.

Thanks Andy! That would suggest very little loss of flow from the pump through the galleries.

wouldn`t the oil pressure relief valve opening sooner drop the oil pressure straight across the rpm range , because it would open
quicker ?

At lower rpms the pump shouldn't be pushing enough oil to push the relief open.
Changing relief spring should change the maximum pressure and volume.
Orange line represents a higher pressure relief.

If at 3000 rpm, the pump starts to push enough oil to crack open the relief, that's the rpm pressure will start to level off.
A high volume pump will open the relief at lower rpm - assuming same oil viscosity, bearing clearances etc

 

[66fs]

It sounds like the piston for the pressure relief valve does not have sharp corners. I would replace that first. And please don't ask me how I know. The pressure relief spring only limits max pressure.

 

[AndyF]

Yes, you might have opened up the restriction to the top end too far which could be why your hot idle oil pressure is so low. I use a clear valve cover to tell me if the oiling to the top end is correct. I don't know any other way to do it. When you start redesigning the oiling system in these engines you have to collect data and make observations or else you can burn up stuff.

 

[famous bob]

It sounds like the piston for the pressure relief valve does not have sharp corners. I would replace that first. And please don't ask me how I know. The pressure relief spring only limits max pressure.

ur hearing wrong-------

 

[famous bob]

Yes, you might have opened up the restriction to the top end too far which could be why your hot idle oil pressure is so low. I use a clear valve cover to tell me if the oiling to the top end is correct. I don't know any other way to do it. When you start redesigning the oiling system in these engines you have to collect data and make observations or else you can burn up stuff.
View attachment 1715264726 View attachment 1715264727

Le me borrow those for a week or two, and I`ll confirm what I `ve got ! L0L -------

 

[fjr]

Andy; wouldn't the oil pressure relief valve opening sooner drop the oil pressure straight across the rpm range , because it would openquicker?

While a relief valve with a lower pressure setpoint would open sooner, it would not have any effect on oil pressure BELOW the relief pressure setpoint. Raising the setpoint reduces the blow-off flow to the sump, which in turn increases the flow to the galleries. Higher oil flow has more pressure loss from fluid friction, which means the pressure "seen" at the pump is higher.

As explained earlier, the oil pressure relief valve only limits the maximum oil pressure and oil pressure is a reflection of pressure losses in the oil system in response to the oil flow generated by the oil pump. You were able to raise your hot oil pressure at idle by shimming the relief valve spring because your high volume oil pump is putting out so much flow at idle that it is causing the relief valve to continuously blow off excess pressure.

I might have mis-stated the restricted oil to the top end. I have full time oiling to the top, and had to restrict it the best I could w/o pulling the heads.
I made the mistake of drilling the lifter galley deal like a guy on here said he did all his engines, it put way too much oil up there, ( big mistake guys, don't do that ) , so I restricted the drilled holes the best I could /under the intake. Then tied the tubes going up , together w/ 1/16'' line, and machined a couple of restrictors to go around the bolts that feed the rockers, therefor closing the opening around the bolts down.
I suspect I still may have a little too much to the top, AND , can drill and install jet type restrictors in the deck surface, if I ever have to pull the heads, which I really don't want to do if I don't have to.

Since andyf found that he was not able to measure a significant variation in pressure at various points in his oil systems, the oil pressure losses in the galleries is normally small from the oil pump to the oil pressure gauge port. In your case, because the oil pump develops so much flow, the oil pressure at the pump is always at the relief valve's setpoint or greater.

Somewhere in your system, the oil flow at one or more branches from the oil galleries is relatively large compared with the flow supplied by the oil pump to the engine. The normal big block pressure gauge location is pretty much at the far end of the oil system and most of the pressure losses occur upstream of the gauge.

If I'm reading the oil system diagram correctly, this is the order that the following branches receive oil flow between the pump and the pressure gauge:

• crankshaft + camshaft bearing #1
• exhaust valve lifter #2
• intake valve lifter #2
• crankshaft + camshaft bearing #2
• intake valve lifter #4
  
• exhaust valve lifter #4
• crankshaft + camshaft bearing #3
• exhaust valve lifter #6
• intake valve lifter #6
• crankshaft + camshaft bearing #4 + L&R rocker shafts
  
• intake valve lifter #8
  
• exhaust valve lifter #8
• crankshaft + camshaft bearing #5
• left main oil gallery (lifters for cylinders 7,5,3,1)

Thanks Andy! That would suggest very little loss of flow from the pump through the oil galleries.

I think you mean there is very little loss of pressure because the oil galleries carry the entire useful flow output of the pump.

 

[famous bob]

While a relief valve with a lower pressure setpoint would open sooner, it would not have any effect on oil pressure BELOW the relief pressure setpoint. Raising the setpoint reduces the blow-off flow to the sump, which in turn increases the flow to the galleries. Higher oil flow has more pressure loss from fluid friction, which means the pressure "seen" at the pump is higher.

As explained earlier, the oil pressure relief valve only limits the maximum oil pressure and oil pressure is a reflection of pressure losses in the oil system in response to the oil flow generated by the oil pump. You were able to raise your hot oil pressure at idle by shimming the relief valve spring because your high volume oil pump is putting out so much flow at idle that it is causing the relief valve to continuously blow off excess pressure.


Since andyf found that he was not able to measure a significant variation in pressure at various points in his oil systems, the oil pressure losses in the galleries is normally small from the oil pump to the oil pressure gauge port. In your case, because the oil pump develops so much flow, the oil pressure at the pump is always at the relief valve's setpoint or greater.

Somewhere in your system, the oil flow at one or more branches from the oil galleries is relatively large compared with the flow supplied by the oil pump to the engine. The normal big block pressure gauge location is pretty much at the far end of the oil system and most of the pressure losses occur upstream of the gauge.

If I'm reading the oil system diagram correctly, this is the order that the following branches receive oil flow between the pump and the pressure gauge:

• crankshaft + camshaft bearing #1
• exhaust valve lifter #2
• intake valve lifter #2
• crankshaft + camshaft bearing #2
• intake valve lifter #4
  
• exhaust valve lifter #4
• crankshaft + camshaft bearing #3
• exhaust valve lifter #6
• intake valve lifter #6
• crankshaft + camshaft bearing #4 + L&R rocker shafts
  
• intake valve lifter #8
  
• exhaust valve lifter #8
• crankshaft + camshaft bearing #5
• left main oil gallery (lifters for cylinders 7,5,3,1)

I think you mean there is very little loss of pressure because the oil galleries carry the entire useful flow output of the pump.

All this makes perfect sense to me , AGREE ALL THE WAY.
I will restrict the full time oiling to the top end even further if I ever have the heads off, I`ve done all I can think of with the engine together in the car. I`m not real worried about the hot idle 18-20 pound pressure, it rises immediately w/ one rpm. Is a little high on up tho.
Might pull one washer out of the relief valve .

 

[famous bob]

So big block? Been 38 years since I touched one LOL. But with the pump at the front of the block and if the measurement pickup is at the rear, that probably explains the low hot idle pressure.... it is at the far end of the system, after all the other pressure drops. How cool is the engine at these cold startups FB ? OK can be pretty cold in some parts during the winter.

I still can't quite see how shimming the relief valve helped it unless the relief valve is always open to some degree.... which I suppose is possible with the very high cold pressure.

A bout 25 here now ! Hate it !

 

[moper]

I think the issue is you have to tune that HV oil pump to work in a clearance situation where it's volume is not needed.

 

[AndyF]

I'd agree. Typically the HV pump puts out more volume than is needed which leads to excessive oil pressure. I've found that for most engines the standard volume pump works better. You might need to add a shim or two to the standard pump to get the pressure where you need it. Other times the HV pump with the soft spring will work. It all depends on how "leaky" the engine is internally.

 

[famous bob]

I'd agree. Typically the HV pump puts out more volume than is needed which leads to excessive oil pressure. I've found that for most engines the standard volume pump works better. You might need to add a shim or two to the standard pump to get the pressure where you need it. Other times the HV pump with the soft spring will work. It all depends on how "leaky" the engine is internally.

Thanks guys !