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Oil pressure vs volume

General engine tech -- Drag Racing to Circle Track

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BobbyB
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Re: Oil pressure vs volume

Post by BobbyB » Thu May 14, 2020 6:43 am

What viscosity oil are you using?

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Re: Oil pressure vs volume

Post by My427stang » Thu May 14, 2020 8:08 am

Assuming a pump can flow more than the engine can bypass, which I think is pretty common unless running a lot of high bypass bearings (needle bearings etc) and loose clearances, the HV portion of the pump really determines idle pressure and the relief spring determines max pressure. Not that you sound like you need an oil pump lesson, but the fact that you are in the ballpark hot and cold of 55-60 is an indicator it's true to yours too (assuming you are seeing those numbers at RPM) and you are running on the relief spring

I personally think that it's plenty of oil pressure, as indicated by the parts looking good, but, if you want a little more pressure, it's just a relief spring change or shim. In the end, you can't change actual volume to the engine without adding pressure, and you can't add pressure without letting more volume go through the galleys.

FWIW, to your situation, I have seen a decent variance in FE HV pumps, all within good enough, but even with the same bearing clearances and associated parts, almost carbon-copy engines in some cases, they vary up 8-10 PSI at RPM
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Re: Oil pressure vs volume

Post by Steve.k » Thu May 14, 2020 8:57 am

Mains set at .0024 rods .0027. Not sure why. Alloy block with no lifter bore bushings maybe thats the loss point.
790408CE-0F4F-4EC5-ADA1-68B7E76D3759.jpeg
Check oil on right. Even starts lower than im used to. I think first fire up seen 65ish.
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Krooser
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Re: Oil pressure vs volume

Post by Krooser » Thu May 14, 2020 11:10 am

Try running less oil.... Keeps the crank from frothing up the oil. I've seen a 6 qt pan gain oil pressure when running two qts low.
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Re: Oil pressure vs volume

Post by piston guy » Thu May 14, 2020 11:44 am

Steve,
I had a similar experience with my "original" 351C aluminum block. As the engine warms up the pressure "goes away" a bit more than an iron block (IMHO) because the bearing clearances change because of the aluminum block. Your PSI numbers indicate ( to me) that you are "up against" the bypass spring. Your oil pressure ( especially with the VASTLY improved Track Boss aluminum 351C block) is easily in the "safe zone" in my experience. I ran a standard volume 351C pump with the Ford 100 PSI spring kit , (actually 80PSI) and never had a problem in my "SK" aluminum block.
The "Smokey Yunick" adage of ten PSI /1,000 rpm was referenced to a GM "spur gear" pump and they are not known for being good "pressure" pumps like a Ford/Chrysler "gerotor " pump is. Smokey was often quoted "out of context" like is famous "use the longest rod possible" which applied to a SBC circle track engine where "porting" the stock SBC head was not allowed.

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Re: Oil pressure vs volume

Post by Steve.k » Thu May 14, 2020 12:49 pm

Ok thanks everyone. Im going to pull pan and valley cover just to check over things. Im using 20w50 for those who asked. Working with Mike jones may change cam to squeak over 800 mark. Thanks Pistonguy did you use lifter bore bushings? This block will not move as much as prior blocks. I made a specific point of watching growth and we cold set rockers at .012 and once hot (160) we checked. Most were at .015 but had a couple at .018. Moved all to .018 and they never changed hot again.

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Re: Oil pressure vs volume

Post by Kevin Johnson » Thu May 14, 2020 12:53 pm

Steve.k wrote:
Wed May 13, 2020 4:00 pm
A lot of guys used to say 10psi per 1000rpm! What do you guys like. Last two days dynoed a sbf oil pressure start at 57-60 hot end up 54-48 at end depending on temp. Melling hv pump priority main oiling 7500rpm limit.
If you read the SAE papers from the early 1950s for the new Buick and Studebaker V8 engines the oil pressure was 40psi for an engine meant to run up to about 4000rpm. Smokey could certainly do simple division.

The engineers also mention frothing and aeration of the oil in the sump and the idea of feeding lifters after the oil had a chance to deaerate. No, they do not mention the Bunsen coefficient or Henry's Law specifically but maybe this was because their audience was engineers who presumably were awake during their physical chemistry lectures.

Good luck with your build.

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Re: Oil pressure vs volume

Post by tuffxf » Thu May 14, 2020 1:01 pm

I'd say 65psi is the relief valve setting if that's what your seeing on cold start up
With alloy blocks or rods the measuring really needs to be done with heated components.
A large oven at a controlled temp will give you an idea where your clearances really are
What lifter bore clearance and type of lifter?
Cheers

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Re: Oil pressure vs volume

Post by Steve.k » Thu May 14, 2020 1:06 pm

tuffxf wrote:
Thu May 14, 2020 1:01 pm
I'd say 65psi is the relief valve setting if that's what your seeing on cold start up
With alloy blocks or rods the measuring really needs to be done with heated components.
A large oven at a controlled temp will give you an idea where your clearances really are
Are the lifter bores bushed , What lifter bore clearance and type of lifter?
Cheers
The lifter bores not bushed and there cam research lifters.

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Re: Oil pressure vs volume

Post by Charliesauto » Thu May 14, 2020 1:52 pm

Steve.k wrote:
Thu May 14, 2020 8:57 am
Mains set at .0024 rods .0027. Not sure why. Alloy block with no lifter bore bushings maybe thats the loss point. 790408CE-0F4F-4EC5-ADA1-68B7E76D3759.jpeg

Check oil on right. Even starts lower than im used to. I think first fire up seen 65ish.
With the aluminum block you could tighten your main clearance to .0018"-.0022 range and probably gain 6-8 psi on the gauge.

Do you know how much lifter to bore clearance you have?

If you ever have the crank out, look at the Daido bearings made in Japan. They have much less eccentricity than Clevites and will dramatically reduce your oil flow with the same vertical clearance. I think you can still get the Daido bearing from Callies.

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Re: Oil pressure vs volume

Post by novafornow » Thu May 14, 2020 2:51 pm

I am using the Daido bearings whenever I can. I am very happy with them.

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Re: Oil pressure vs volume

Post by David Redszus » Thu May 14, 2020 5:10 pm

Oil volume is much more important than pressure. Oil pressure is merely a surrogate for estimated volume through the bearings.

Given bearing dimensions, clearances, oil viscosity at operating temperature, and engine rpm, it is possible to calculate
oil flow volume. Given oil specific gravity, the oil mass flow can be determined which is necessary to calculate the heat
transfer from the bearings into the oil. The oil temperature will also determine the minimum oil film thickness.

An alternative method is to measure the bearing cap temperatures directly.

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Re: Oil pressure vs volume

Post by af2 » Thu May 14, 2020 5:18 pm

That box is making me wonder??? Is there any way oil can get in besides over the top? Front sump?
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Re: Oil pressure vs volume

Post by Steve.k » Thu May 14, 2020 6:26 pm

It has trap doors all the way around that swing in.

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Re: Oil pressure vs volume

Post by Kevin Johnson » Thu May 14, 2020 8:11 pm

Steve.k wrote:
Thu May 14, 2020 6:26 pm
It has trap doors all the way around that swing in.
It is possible that windage flow is being directed into the interior of the box (inward facing ledges exacerbate/capture this) and this would tend to dynamically work against the inward opening of the doors on that "half" of the box. The oil would tend to be pushed up on that side of the pan by the rotational flow in any event. The gaps at the end of the corners of the box with the sump reservoir walls are narrow and would resist flow to the opposite side. These factors together increase the possibility of small vortexes occurring on the downstroke side through the inward opening doors.

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