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Oil pressure vs volume

General engine tech -- Drag Racing to Circle Track

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Steve.k
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Oil pressure vs volume

Post by Steve.k » 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.

ClassAct
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Re: Oil pressure vs volume

Post by ClassAct » Wed May 13, 2020 4:27 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.
It totally depends on the oiling system, how it’s laid out etc.

swampbuggy
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Re: Oil pressure vs volume

Post by swampbuggy » Wed May 13, 2020 5:26 pm

Steve, you are in great shape with those numbers, be happy ! Mark H.

Kdub
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Re: Oil pressure vs volume

Post by Kdub » Wed May 13, 2020 6:05 pm

In a small block Ford you are good to go with those numbers. Using a different brand of oil my help the oil pressure, but it's the oil pressure at RPM is what is important.

Steve.k
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Re: Oil pressure vs volume

Post by Steve.k » Wed May 13, 2020 6:09 pm

We tore engine down last time after short runs. It was all good. Ive never seen it that low so wasn’t sure.

RykerMcdermot
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Re: Oil pressure vs volume

Post by RykerMcdermot » Wed May 13, 2020 6:39 pm

When in doubt, test it : )

Steve.k
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Re: Oil pressure vs volume

Post by Steve.k » Wed May 13, 2020 7:33 pm

This block feeds mains first then top. Every other sbf ive seen with hv wet style pump runs close to 70 psi cold. This one never gets past 62. Im just wondering cause it puts oil at crank first and obviously more pressure losses would be there that the reason.

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Re: Oil pressure vs volume

Post by BILL-C » Wed May 13, 2020 7:50 pm

You probably have an oil pan issue. The oil pressure should climb with rpm until pressure relief opens and stays steady. That drop in pressure at end is concerning. It usually means you are sucking air. We NEVER use HV pumps in our sb ford builds. What is your stroke on crank?
Carlquist Competition Engines

rustbucket79
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Re: Oil pressure vs volume

Post by rustbucket79 » Wed May 13, 2020 11:10 pm

Have you tried adding a half quart or so?

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Re: Oil pressure vs volume

Post by Steve.k » Wed May 13, 2020 11:34 pm

Its a 6quart We were putting 7 no difference.
Pan with trap doors and box to suck out of. This has same oiling basically as windsor.
B75F82FA-9914-473C-BA64-378C5BD38278.jpeg
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rustbucket79
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Re: Oil pressure vs volume

Post by rustbucket79 » Thu May 14, 2020 12:04 am

I would question the "box" as being restrictive but the extra litre should have overcome.

Any possibility of the pickup being too close? I've had issues with too much oil, but the pressure fell off to nearly nothing quite quickly, doesn't sound like your issue.

Maybe try a different oil filter before diving deeper into the engine?

bob460
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Re: Oil pressure vs volume

Post by bob460 » Thu May 14, 2020 12:25 am

Any type of windage tray being used?.........also i would weld plates where the box welds are so there's no gaps.....something like this https://scontent.fmel6-1.fna.fbcdn.net/ ... e=5EE06592

tuffxf
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Re: Oil pressure vs volume

Post by tuffxf » Thu May 14, 2020 2:41 am

It’s a positive displacement pump, shouldn’t drop with rpm, should stay the same if relief valve is a good design.
Need to figure out if drop at rpm is due to temp or rpm, if it’s temp then you have an oil pressure loss through a clearance issue somewhere.
If it’s only rpm then it’s a pickup, pan, windage, drainback type of deal.
What’s It do at rpm with cooler oil?
Cast iron or alloy block?
Good design can live at lower pressures then what we used to use but oil pressure shouldn’t drop as rpm rises
Cheers

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Re: Oil pressure vs volume

Post by tuffxf » Thu May 14, 2020 4:41 am

Do you have a vac pump on it Steve?
Cheers

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Re: Oil pressure vs volume

Post by BILL-C » Thu May 14, 2020 6:37 am

A vacuum pump will make gauge readings drop for sure. Usually .5 -.7 psi per " of vacuum.
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