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Old 01-05-2011, 12:19 AM   #1
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Default New engine low oil pressure

So having spent way more on this car than I intended to everything is installed
The engine is a built motor with slightly looser tolerances. It is running one of the ported oil pumps with billet gears from Boundary engineering(standard pressure relief spring-not shimmed).
The engine has had oil pressure since start up but it has always read pretty low. The oil pressure on start up on the oil pressure gauge(aftermarket gauge with sender in the stock location in the head) read about 30 and then would drop to about 20psi(as the oil warms) at anything over 2K rpm. it has about 8-10psi at idle. So we hooked up a mechanical gauge from the block and the engine only gets up to 40psi even up to 6K rpm. I haven't revved it any higher than that.
So, I know from searching that miata motors run lower oil pressure than the subarus I am used to and flow is more important than pressure. However, this still seems a little low and I was going to rev the motor to 8K or so.
I am not particularly experienced with miatas and so does anyone think this is safe? Should we go ahead and tune the engine?
If it seems too low what is the source-partially stuck open pressure relief valve? Bad oil pump seems unlikely, I don't think the engine is loose enough to account for this low a reading.
Any thoughts you might have, I would rather not pull the engine but it feels like it is going to be necessary.
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Old 01-05-2011, 01:41 AM   #2
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What kind of head?
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Old 01-05-2011, 01:41 AM   #3
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What year of head I mean.
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Old 01-05-2011, 11:02 AM   #4
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BP4W from 05 MSM
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Old 01-05-2011, 11:27 AM   #5
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In for answer.
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Old 01-05-2011, 11:35 AM   #6
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One thing, the stock pressure sensor isn't in the head. Before getting too worried about it, order the BSP oil pressure sender adapter from FM or the remote oil pressure sender kit from advanced autosports to get pressure from the proper location by the oil filter. I don't know for certain if it would make a difference, but it makes sense that it would.
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Old 01-05-2011, 11:37 AM   #7
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My '95 idled at 10-13 psi when warm, before and after my build. My NB idles around 9-10 psi, engine internals are stock. Rotella T used in both cars. My '95 would gain 10 psi for every 1,000 RPM but I can't remember where it maxed out. My NB does the same thing and seems to max out at 45 psi. All readings taken from a sandwich plate at the oil filter and with AutoMeter gauges.

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Old 01-05-2011, 11:44 AM   #8
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When hot: mine idles at 8-15psi. Maxes out around 45/50psi. I have a VVT head. Stock sensor location. Miata roadster billet opg.
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Old 01-05-2011, 11:46 AM   #9
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I'm with RotorNut... after installing the Advanced Autosports oil pressure sender kit and grounding the gauge properly for the DB gauges I'm around 10 to 15 psi when warm at idle. It is a real time sweep gauge and pegs up to 40-45 psi at singing speed. Thought it read low but have come to find it is normal. I went this route for the '96 as I wanted real time working pressures and not the good ole dummy gauge.
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Old 01-05-2011, 12:46 PM   #10
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Hmm I feel a little better
when I said block I should have said the sandwich plate adapter at the oil filter.
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Old 01-05-2011, 12:47 PM   #11
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accidental repost
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Old 01-05-2011, 12:49 PM   #12
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That's about right, it depends alot on the viscosity, but the relief valve will be fairly open at about 45-50. You probably won't see over 60 without shims in the pump though.

The only failure mode that you can possibly have is debris in your oil pump relief valve, but it definitely doesn't sound like you have that.
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Old 01-05-2011, 01:26 PM   #13
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Yeah it has only been run for the equivalent of a couple of miles and so we drained the oil and there was no visible material in the oil.
Ok just different from what I am used to then.
One last question. Should there be a further increase in oil pressure as the revs go from 6-8K?
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Old 01-05-2011, 03:21 PM   #14
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Probably not, once you hit the "max" the relief valve should control the pressure pretty well. You might get a little more, but it won't be another 30% or anything.
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Old 01-05-2011, 04:10 PM   #15
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pressure relief valve doesn't have a lot of "gain" - the range of regulated pressure may be 20-30 psi.
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Old 01-05-2011, 05:23 PM   #16
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For high boost should we be running a shimmed pump for more oil pressure?
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Old 01-05-2011, 06:47 PM   #17
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Quote:
Originally Posted by Faeflora View Post

For high boost should we be running a shimmed pump for more oil pressure?
Yeah, if I wanted additional reassurance would it be wise to add a couple of shims to raise the oil pressure?
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Old 01-05-2011, 07:01 PM   #18
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Quote:
Originally Posted by JasonC SBB View Post
pressure relief valve doesn't have a lot of "gain" - the range of regulated pressure may be 20-30 psi.
Yea its pretty T dependent! It is pretty steady though once everything is warmed up.

Quote:
For high boost should we be running a shimmed pump for more oil pressure?
Typically +14 is what I recommend but watch your turbo seals. Make sure you choose an appropriate restriction. If you're unsure whats best you can contact the turbo manufacturer and they probably have a chart that will give you exactly what you need. If not, I can probably get you what you want from some calculations but I still need to know what the turbo requires as far as max pressure and required flow.
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