My engine loves high oil pressure

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Originally Posted By: used_0il


I'm glad someone else mentioned 90 psi on small block Fords, I chickened out.

Some Cleveland owners are stretching the pump spring or shimming it to 100 psi......."



I am in the longtime habit of driving my vintage Shelby Mustang(s) equipped with a vintage Paxton supercharger, and my '65 HiPo Mustamg K code in high speed endurance races. Typically you are redlining, going flat out in top gear (4th for me) for about 130 miles, or until your gas tank runs dry.

The last thing I want to be thinking about is lubrication issues. Small block Fords certainly can be ran normally on normal oil pressure without any issues. But for extended high rpm usage, especially with the 289 engines, they will thrive on high oil pressure. Yes you do lose 3 or 4 horsepower by running 80+ psi . But that is about the only drawback I know of. Of course, oil pump shafts need to be upgraded.

High volume pumps with their increased flow, are much better at removing excess heat from the main and rod bearings than a conventional pump with lower pressure and volume.

I use mobil 1 15w-50 in the summer, and most of the year, 0w-40 when the air temperature is below 30 F.

Z.
 
Originally Posted By: used_0il
..His reply was that he was not worried because he takes the oil pan off and checks the bearings after every race..


Not sure how that relates to your road going diesels' topic but I'm sure grateful not to have to drop my pans that often!
 
The reason I mentioned pressure raising the boiling point of oil
in my topic starter;

It was stated in another thread that plain bearings once primed
can self-pump their own oil.

That would mean they reduce the oil pressure being delivered
to the oil gallery.

A reduction in pressure would result in a lower boiling point.

The oil picks up heat in the bearing cavity and also from its own
operating friction from viscous drag.

The added pressure of the lubricant may prevent the oil from boiling
while in its duty cycle.
 
Originally Posted By: SHOZ
Even hot the oil sometimes will hit 90 lbs at 7k rpm. No real difference between 5w30 and 0w40 M1 as far as pressure goes.

I'm afraid you're mistaken. OP will be considerably higher with M1 0W-40 (HTHSV 3.85cP) vs a typical 5W-30 (HTHSV 3.0-3.2cP).
If you're not seeing it then you're not comparing at the same oil temperature and engine rpm.
 
I'm seeing what my gauge says. I peak oil pressure is always at 7k rpm when warm. Oil temp is usually between 190-200F.

The pump pressure relief sets the peak pressure on this motor.
 
Originally Posted By: CATERHAM
The pump pressure relief valve sets the peak system back-pressure in all engines. Once up to temperature your maximum OP should be below the by-pass setting on a 5W-30.


Can an engine design allow running on the pressure relief setting at just about everything but idle? My BMW K75C shows 65psi at 2000 RPM all the way to 8500 RPM when warm. 1000 RPM hot idle is 35 PSI. This is on 10W-40 oil, not the recommended 20W-50.

It must be sufficient..the bike has 144,000 miles on it.
 
Last edited:
Originally Posted By: ammolab
Originally Posted By: CATERHAM
The pump pressure relief valve sets the peak system back-pressure in all engines. Once up to temperature your maximum OP should be below the by-pass setting on a 5W-30.


Can an engine design allow running on the pressure relief setting at just about everything but idle? My BMW K75C shows 65psi at 2000 RPM all the way to 8500 RPM when warm. 1000 RPM hot idle is 35 PSI. This is on 10W-40 oil, not the recommended 20W-50.

It must be sufficient..the bike has 144,000 miles on it.



if you don't know the psi setting of your pressure relief valve, then you cannot draw any conclusion based on your psi observations.

Even with a pressure relief valve set at, for example 75 psi, your engine may only be capable of maintaining a 65 psi oil pressure at any rpm. It is erroneous to think the oil pressure should rise with increased rpm in a linear fashion. With increased rpm the engine is "needing" the increased output of the oil pump just to maintain a constant pressure. Centrifugal forces are expelling the oil from the rod and main bearings at ever increasing rates that match the oil pumps increased output as the rpm goes up. Most modern (post WW II) engine designs do not depend on the pressure relief valve to control normal oil pressures. The design of the engine does that.

In my case, with a Ford 289 HiPo engine with a HV oil pump, I have the adjustable pressure relief valve set at 90 psi. Only when the oil is cold could I reach that mark, and engage the relief valve. And then only by foolishly revving a cold engine (not going to happen). When the oil has reached operating temperatures my oil pressure peaks at 78 - 80 psi at any rpm over 2,500 - 3,000. The pressure relief valve is not controlling the pressure at the 80 psi level, the engine design is.

Meaning, the ever increasing volume of oil bring pumped as the rpm is increasing, is being perfectly matched by the increasing needs of the engine for more oil. It's a beautiful thing.

I don't know the formulas for matching oil pump capacity to the bearing area being lubricated. But a well trained engineer could recite them in his sleep.

The wild card in all this is bearing clearances. If clearances are allowed to increase beyond factory specified limits, the oil pump cannot keep up. Oil pressure is reduced, and engine life is reduced.

Z.
 
I think CATERHAM is going the in same way I was thinking.
Or more likely, the other way around.

This is what I think he is telling us;

As long as your observed oil pressure is "at or higher" than the oil pump's by-pass
setting, your oil is being by-passed.

Here is how that would work on my rebuilt SBCs with a 62 psi pump spring;

With 15W50 at 6,500 rpm the oil pressure is 80 psi.
With 15W40 at 6,500 rpm the oil pressure is 80 psi.
With SAE30 at 6,500 rpm the oil pressure is 70 psi.
With SAE20 at 6,500 rpm the oil pressure is 62 psi.
With SAE20 at 5,500 rpm the oil pressure is 54 psi.

CATERHAM would likely say that at 6,500 rpm the pump is by-passing SAE20 oil.

I would rather him answer that question than put words in his mouth.
 
Originally Posted By: used_0il
I think CATERHAM is going the in same way I was thinking. Or more likely, the other way around.

This is what I think he is telling us; As long as your observed o........................il.

I would rather him answer that question than put words in his mouth.


What is your point here OP ? Why not go and ask the engine builder who rebuilt your SBC ? He may have a clue.
 
What's your pump shifting ?
8GPM ?

Given the 6,500RPM pressures that you are recording, the difference in oil pump shaft power consumption between the 20 and the 15W50 at 6,500 RPM is about 100 watts (1 hp is 748 watts).

Given that the bearings will only swallow/take that oil which they need to take to replace side leakage, and the (back)pressure is the artifact of them not wanting/needing to take that oil, and it having to go through other places like squirters (and relief valves) at higher pressure to get the pump flow back to the sump, why would anyone consider the optimum is to drop viscosity until all of the oil is pumped through the bearings ?

Sommerfeld number drops (thats the basis of the lower axis on the Stribeck curve), minimum oil film thickness drops, and side leakage increases (which is where you are putting the oil that's being pumped through the bearings)

Technically correct answer is to optimise the oil pump displacement such that the pump matches the oil supply needs, and has the right pressure to run squirters and adjusters...cue the variable displacement pump
 
The figures are not observed, a hypothetical situation, but
not far off from what I have observed in several engines.

The reduction in pressure from the lighter SAE20 oil
could then be a result of a higher volume of oil going through
places other than the plain bearings, but not through the pump
by-pass.

Was putting the same pressure for the 15W50 and 15W40 a mistake
on my part, or a "rake on a dark path",
just to see who steps on it?
 
well you need to start putting [hypothetical] ... [/hypothetical] on either side of your statements that may or may not be observations or represent facts.

I'm over your trollplay.

and if Farmer Brown only puts HV pumps in his engines, then Farmer Brown is an idiot.
 
Originally Posted By: ammolab
Originally Posted By: CATERHAM
The pump pressure relief valve sets the peak system back-pressure in all engines. Once up to temperature your maximum OP should be below the by-pass setting on a 5W-30.


Can an engine design allow running on the pressure relief setting at just about everything but idle? My BMW K75C shows 65psi at 2000 RPM all the way to 8500 RPM when warm. 1000 RPM hot idle is 35 PSI. This is on 10W-40 oil, not the recommended 20W-50.

It must be sufficient..the bike has 144,000 miles on it.

Yes it's more than sufficient but why the question I would want to know is why your OP always max's out at 65 psi?
Your oil temp's may not be getting very high.
65 psi may be the by-pass point of your oil pump or the OP gauge may be pegged at 65 psi (don't laugh it's not uncommon).

If you can get the recommended min' OP at elevated rpms from BMW that should help answer your question.
 
Lets look at the oil pressure question from two other hypothetical tests;

To eliminate the variable that VII multi-grade engine oils would have
I've selected four mono grades.
All of the oils are preheated to 100C and remain there for the experiment.

SAE20
SAE30
SAE40
SAE50

We remove the oil pump and hook up a supply of each of the four lubricants
directly to the engine.

Then we take a bar and turn the engine over by hand at 15 RPM.

We measure the amount of oil that flowed through the engine in one minute
and the lighter oils have flowed more.

Now we put the oil pump back on and perform the same experiment.

All of the oils have flowed the same volume after one minute.

The obvious reason is that the oil pump is turning relative to the engine
and pumps the same amount of oil per revolution at 15 RPM as it would
at 6,500 rpm.

Since the pump is a positive displacement type, the viscosity of the oil
did not change the flow rate.

In addition to your engine being a stove and a wash machine,
it is also a clock that starts and stops as it rotates.

The big end of the connecting rod is the best place to illustrate
one of the time factors.

AT BDC and TDC, the piston and connecting rod both slow in relation to the
engine speed.

When the bearing is stopped at the red light, oil is still flowing around
and through the bearing cavity.

Time has not stopped for the connecting rod, because it can observe traffic
(the lubricant) moving in the other direction.

With the connecting rod removed, the journal still slows and stops at TDC and BDC.

The valve train does the same and there is wind-up and let-go in both the cam
and crank shafts as loads are applied and released.

The other time factor results in the oil pressure rising with RPM.

Because of the fact we have a fixed positive displacement pump that turns
at a speed relative to the engine RPM, the reduced time the engine has
to bleed off the same volume of oil is decreased.

The result of that is increased oil pressure with RPM.

To keep the pressure from rising too far, a pressure relief valve is added
to the oil pump.

One other method is to control the viscosity of the engine oil.

The notion of reducing the size or the output volume of the oil pump as RPM
increases to control pressure is not the way this Farmer Brown would
address the issue.
 
Originally Posted By: used_0il

The notion of reducing the size or the output volume of the oil pump as RPM
increases to control pressure is not the way this Farmer Brown would
address the issue.


I've never heard of anybody actually practising this, but I have certainly seen the opposite: People fitting HV pumps to their engine so they have higher oil pressure. A popular "old timer" mod/"upgrade".

I mentioned this to CATERHAM before but my buddy's dad's S10 we used to wrench on quite a bit had an HV pump in a 350 with stock bearing clearances. It would go well beyond the relief pressure on the pump when cold.
 
Originally Posted By: OVERKILL

I mentioned this to CATERHAM before but my buddy's dad's S10 we used to wrench on quite a bit had an HV pump in a 350 with stock bearing clearances. It would go well beyond the relief pressure on the pump when cold.

I have noticed this effect myself on occasion (but not consistently) on a stock pump if an engine is rev'd very high with cold oil, something I generally don't do.
In my case I've attributed it to a sticking by-pass valve but I presume it can also happen if the capacity of the fully open by-pass valve is exceeded with the right combination of thick oil and high rev's.
 
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