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Oil Drainback/Windage Issues

General engine tech -- Drag Racing to Circle Track

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matt69nova
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Oil Drainback/Windage Issues

Post by matt69nova »

Seeking feedback on a falling oil pressure problem as shown in the Racepak graph below, where the light blue line is the pressure. Oil pressure starts out good at 75psi at the line, but as you can see gradually falls down to roughly 30psi towards the end of the run. This is a Procharged SBC, Dart Little M block, Moroso billet pump, solid roller, 9" tire stick car currently running in the mid 10's. The car is brand new, so the 1st gear data is pretty useless, as I'm still trying to figure out the suspension and clutch. 20W-50 Brad Penn oil, no external drainback lines, no oil restrictors, Stef's affordable aluminum pan with partial windage screen and baffling, no crank scraper. Pan claims a 6qt capacity, plus I have a 2qt. accumulator, so there's currently 8qts total in the engine. If I get to run the car again this year, I'm going to try and reduce the volume 1/2qt. at a time to see if it has any affect. Does this appear to be a windage and/or drainback issue, an excess oil volumbus problem, or do I have something else going on here?

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1972ho
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Re: Oil Drainback/Windage Issues

Post by 1972ho »

Maybe you try to make a run without the windage tray to see if it holds pressure I just did that on a cleveland but my oil pressure was dropping in the first .60ft my oil light was coming on.So I have since removed the tray and now my oil pressure lights not coming on but I was also toasting bearings.
ClassAct
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Re: Oil Drainback/Windage Issues

Post by ClassAct »

Take the accumulator off. You don’t need all that crap.
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Re: Oil Drainback/Windage Issues

Post by PRH »

Might be worth a trip to the chassis dyno to see if it does the same thing with the car in a static condition(no G forces).

Could also try it with the accumulator shut off while you’re there.
See if that’s having any affect.

You didn’t say what the stroke was.

Any vacuum pump?
Somewhat handy with a die grinder.
matt69nova
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Re: Oil Drainback/Windage Issues

Post by matt69nova »

No vacuum pump, just two -12 lines to separate breather cans. 3.750” stroke. If we do get to go to the track once more this year, I’m going to drain and shut off the accumulator, and drain 2 qts from the engine for a total of 6. Then if there’s no improvement I’ll remove 1/2qt at a time down to 5qt to see if it helps. Are external drainback lines in the cylinder heads worth the effort? I’m sure it’s something simple I’m missing.
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Re: Oil Drainback/Windage Issues

Post by PRH »

I don’t have a ton of high rpm SBC experience, but on the ones I built I used the Canton pan with the power pouch.
Rock steady oil pressure on the dyno....... and no reported pressure problems or oiling issues in the car.
Last edited by PRH on Thu Aug 26, 2021 6:19 pm, edited 1 time in total.
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Re: Oil Drainback/Windage Issues

Post by miniv8 »

How much dome pressure is there on the accumulator?
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matt69nova
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Re: Oil Drainback/Windage Issues

Post by matt69nova »

miniv8 wrote: Thu Aug 26, 2021 6:18 pm How much dome pressure is there on the accumulator?
8psi on the accumulator.
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Re: Oil Drainback/Windage Issues

Post by rebelyell »

Is the pump too efficient?
Is it pumping so much oil that it's accumulating so much in the valve covers etc while not returning enough to the pickup?
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Re: Oil Drainback/Windage Issues

Post by mag2555 »

My experience has been that a very tight fitting crank scraper and a baffled oil pan works better then the latter and a windage tray.
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
matt69nova
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Re: Oil Drainback/Windage Issues

Post by matt69nova »

rebelyell wrote: Thu Aug 26, 2021 11:37 pm Is the pump too efficient?
Is it pumping so much oil that it's accumulating so much in the valve covers etc while not returning enough to the pickup?
This was a concern of mine. I question if the Moroso pump is pumping too much oil to the top end without adequate time to drain back. Also, I have been running the car around 160*, and with 20W50 oil, I don't know if the oil has adequate temperature to thin out and allow easier drainback. Also why I had considered adding external drainback lines.
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Re: Oil Drainback/Windage Issues

Post by ClassAct »

matt69nova wrote: Fri Aug 27, 2021 7:07 am
rebelyell wrote: Thu Aug 26, 2021 11:37 pm Is the pump too efficient?
Is it pumping so much oil that it's accumulating so much in the valve covers etc while not returning enough to the pickup?
This was a concern of mine. I question if the Moroso pump is pumping too much oil to the top end without adequate time to drain back. Also, I have been running the car around 160*, and with 20W50 oil, I don't know if the oil has adequate temperature to thin out and allow easier drainback. Also why I had considered adding external drainback lines.
Unless you are running 1970’s bearing clearances you don’t need that thick oil. Even if you are running the engine at 200* you don’t need that. It also doesn’t matter what size the oil pump is because it can only pump as much oil as the system requires. I seriously doubt the heads are holding all that oil. I say gain you don’t need that accumulator. I’ve pulled many of them off for this very reason. If the pan is baffled correctly and you have the pickup the correct distance from the floor of the pan you don’t need that bulky thing.

That’s another thing. On pans that hold under 8 quarts of oil I always set the pickup between .250 and .300 from the floor. Any more than that and you’ll see the oil pressure go away during a run.

That’s just what I’ve found over the years.

EDIT: I just reread your OP and I see what pan you have. I have never seen a pan with that name on it worth a crap. In 1996 I had them build me a custom full length box pan with a full length kick out. I told them what I was doing and what I thought it should look like. Even faxed them a drawing of what I thought the baffling should look like. When it showed up there were no baffles. Just two walls with a rear facing lip in them and trap doors. I took some measurements and the first wall (they called it a baffle but that’s not what I called it, as it was a wall and nothing more) was too far forward. So any time you hit the brakes what little oil was still in the pan would go to the wall and uncover the pick up. There was no baffling to keep the pick up covered when accelerating either. So when you left the oil would climb the back wall of the pan and uncover (at least partially) the pickup. Before I ever made a pass with it I called them and told them my concerns. And of course, they claimed it was a 6 quart pan. So there wasn’t much oil in the pan to start with as it was a box style pan. And they told me it was the latest and greatest technology there was and to send it. BTW, it had a screen windage tray in the pan. So I made a pass in it and in the first run it got a rod bearing. The long and short of it was I spent about 20 hours unscrewing their jacked up, unbaffled, poorly designed pan. So I’d ditch the accumulator and take a long, hard look at that pan and see where the oil goes when you leave. If it’s as bad as their pan I used and have seen over the years it needs to be fixed.
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Re: Oil Drainback/Windage Issues

Post by RDY4WAR »

That 50 grade molasses is part of the issue. Unless the car was idling the entire time in the lanes, the oil temp is likely <140*F pulling into the burnout box, <160*F at the line, and max of probably 180*F on the top end. At those temperatures, that 20W-50 oil's viscosity is in the 50-150 cSt range. For comparison, maple syrup is ~150 cSt at room temperature. That high viscosity is harder to pump and drains back much slower. It's also more susceptible to aeration and increases hydrodynamic friction.

What's likely happening is the oil is being pumped faster than it can drain back. All of that oil lingering around is susceptible to windage in the crankcase. The pan could have poor baffling as well. The pressure is likely dropping due to aeration from the pickup sucking air. Your pressure at idle doesn't help matters as the capacity for entrained air increases exponentially above ~65 psi which is why that's the typical bypass point for most oil pumps. There's no proof that pressure higher than that is beneficial, even in race engines turning >10k rpm. It just robs power and increases aeration.

My drag engine isn't boosted, but I use an OEM stock volume, stock pressure pump and 0W-12 oil. Oil pressure at the line is just 7-8 psi at 1000 rpm idle and 30-40 psi down the track. No windage tray, just a good scraper. No issues at all.

I agree with others to ditch the accumulator. It's doing nothing for you.
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Re: Oil Drainback/Windage Issues

Post by rebelyell »

ishihara-johnson crank scrapers

https://www.crank-scrapers.com/
matt69nova
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Re: Oil Drainback/Windage Issues

Post by matt69nova »

Thank you guys, these are all great things to think about.

I should have included the bearing clearances. The mains are 0.0030-0.0031 and the rods are 0.0026-0.0027 (steel rods). The recommendation for 20W50 oil came from Brad Penn. I don't mind running the car a little warmer, or trying a lighter weight oil. I'll drain and leave the accumulator shut off (and remove the corresponding amount of oil). These are easy things to try.

I will look at oil pans. I would rather buy something off the shelf, as this isn't max effort. I like the Moroso 21015 or Moroso 21234 but I am open to suggestions.

This winter when I can pull the motor I will add the crank scraper along with possibly a new pan.
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