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Oil Pressure Drop at Higher RPM

Posted By charliemccraney 5 Years Ago
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charliemccraney
Posted 5 Years Ago
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Ted (5/21/2016)
charliemccraney (5/20/2016)
I watched my in truck video during the last pass I made, paying attention to the oil gauge.  The pressure drops a lot, not slightly, by the time I'm at the end of the track so that is something I will have to resolve before I race again.
I installed a gate, made out of piano hinge, on the baffle.  Maybe that is not allowing oil to flow as well back to the pickup.  Will get a pan gasket set and check things out.

Charlie. As long as the oil pan gate door swings to the back, you should be good in that regard.  How many quarts of oil do you carry within the pan including what’s in the filter?


Ted, you asked this in http://forums.y-blocksforever.com/Topic119711-1.aspx, so I'll start a new thread to answer and hopefully resolve the issue.

The gate door does swing to the back.  I normally run 6 quarts total, according to the shop manual.
In addition to the high rpm drop, which is significant, I notice that the pressure starts to flutter at about 2300rpm.  This is consistent whether the oil is hot or cold but of course, the pressure is higher when cold.

I did add a quart, for 7 total.  It changed nothing with the flutter and there is not a good place to test the higher rpm aspect close to home.

The plan is to pull the oil pan to verify pickup clearance, 1/4" to 3/8", try to devise a way to observe that the gate is working properly or remove it altogether for testing, the factory baffle will still be in place, and try an additional quart or two.

Here's the post about installing the gate, http://forums.y-blocksforever.com/Topic1469.aspx?.  Looking back at that, I may need to trim more off of the baffle.   It was designed for low rpm street use, so it's possible it doesn't allow enough flow back to the pickup in performance situations.  Also possible is without additional clearance under the baffle, there is not enough surface area for the oil to open the gate as effectively as I thought.



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Ted
Posted 5 Years Ago
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Charlie.  This sounds like a cavitation issue.  Assuming the oil pump pickup to pan clearance is okay, then two other things come to mind.  First would be an air leak on the inlet side of the oil pump.  Next would simply be a faulty oil pump or at least a problem in the oil pressure relief area of the pump.  Do you have some specific oil pressure numbers in regards to the variance?

Lorena, Texas (South of Waco)


charliemccraney
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The flutter results in about a 5psi variance, around 40psi and it doesn't seem to drop, just bounce around at typical street rpm.

In my video, by the end of the track, pressure had dropped to about 10psi.  That was in the neighborhood of 6000rpm.

When the engine is hot, it can't seem to get much above 45psi and it has always been that way, with two oil pumps, one a spur gear and the other gerotor.  The spur gear pump was a remanufactured unit.  The gerotor was rebuilt with the Melling kit and all clearances are in spec.  The gerotor is currently installed.  The relief spring is shimmed about 1/8".  It will achieve about 80psi, cold.



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charliemccraney
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The inlet tube nut was a little loose.  I tightened it and there was no difference with the flutter.  I did notice that whenever I let off the gas, the pressure jumps about 5psi



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Ted
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Charlie.  That drop in oil pressure when accelerating and then increasing when the load is taken off the engine points me to main bearing clearances being on the ‘big’ side.  Increasing the oil viscosity could be one way of determining this without an actual engine tear down.

Lorena, Texas (South of Waco)


charliemccraney
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Mains were .0025, but that was determined with plastigauge, which I now know is not the best to use.


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speedpro56
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Charlie, make sure the large nut on the oil pan tube going into the oil pump is snug. Caught mine sucking just enough air to cause a flutter. Not saying this is your problem but an easy check.


-Gary Burnette-


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I checked that nut.  It didn't help.  I did change from 20/50 to 15/40 last year.  So maybe I do need to go back.

About 5 3/4 quarts drained.  That seems about right considering the filter and other places oil might hang out.

I marked the pickup tube and pan before removal so I had a reference for their proper relation once removed.  The pickup is positioned about the best it can be.  The only way I can make it better is to flatten the bottom of the pan and try to bend the pickup tube for the new depth.  If it's really necessary to go to such measures, I'm just going to send a pan to a place like Canton Racing for proper modification and additional capacity.  It's hard to see in the pictures, but the pick up is tilted so it is higher in the front and lower in the rear.  This makes sense, given it's position right over the 2nd drop, to the lowest section of the pan.  This does seem to indicate that it could start ingesting air even if there is a couple quarts in the pan.