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Acceptable 328 oil pressure levels?

Discussion in 'Technical Q&A' started by rob lay, Feb 20, 2004.

  1. f355spider

    f355spider F1 World Champ
    Rossa Subscribed Owner

    May 29, 2001
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    Hugh G. Rection
    BTW, I am listening, and intend to switch to a 5w-30 and probably 0w-30 Mobil 1 just to see the oil pressure differences.
     
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  3. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
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    Hans E. Hansen
    Dave: Ask Carlo. The regulator is sort of a pop off valve, in that it bleeds off pressure only when it reaches a pre-set level. It has absolutely no effect on either pressure or volume until the max pressure is reached.
     
  4. AEHaas

    AEHaas Formula 3

    May 9, 2003
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    Ali E. Haas
    If you are getting 100 PSI at idle and your pop off is also at 100 PSI then your engine will never increase oil flow as the RPM goes up. If your pump is putting out 1 qt. per min at idle into your engine, it will put out 1 qt per min. at 3,000 RPM and 1 qt. per min at 6,000 RPM.

    I used the phrase "into your engine" because the pump will in fact increase output with higher RPM but all the additional flow will go straight back to the sump and bypass the engine because of the pop off valve.

    If you use a thin enough oil then your pressure must go down. It will do so only because the flow rate is going up. It is an inverse relationship. The flow rate will increase as the RPM until the pop off pressure is reached, after which there will be no additional flow of oil to the engine despite more RPM.

    My Maranello idles at 600 RPM. There is no load and the theoretical pressure of oil needed even with a load is 6 PSI. I am getting 30 PSI with 20W oil. As I step on the gas the torque increases as does the pressure and the flow giving me 70 PSI at 2,000. Again, The manual states the target for that pressure is 6,000 RPM so I still need a thinner oil to comply with the manual's stated RPM/Pressure goals. This is for the around town driving temperatures that my engine reaches. Your needs depend on your driving habits. My oil temperature runs around 180F. I get 15 MPG around town. I can burn rubber by stepping on the gas in 1st, 2nd and 3rd without even popping the clutch.

    aehaas
     
  5. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
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    Let's see.... You're saying that if the engine idles with, say 10psi, then oil flow at 100psi at 6000 rpm would be adequate, but it's inadequate if it idles at 100psi? 100psi at 6000rpm will result in the same flow, regardless of what was going on at idle. That was just plain weird.

    Oil pressure is measured at the actual entrance to the engine, after passing thru the cooler and filter. It's measured at a 5/8" (approximate - it's the dia of my finger, as that is what I used to plug the hole when I was scraping gaskets.) hole on the top of the block. ALL oil lubricating the engine enters here. Fluid dynamics are not quite like electricity, but you can draw some parallels to Ohm's law. First, you can't have pressure w/o some sort of restriction. Try to measure pressure at the OPEN end of a garden hose. The restriction, in this case, is the engine's lubricating system, and all it's various bearing clearances, etc. You apply a pressure against this restriction, and a specific amount of oil will flow. Period. More pressure, more flow. (However, unlike electicity, it's not exactly linear.) If you apply 100psi to this orifice, you will have more than adequate flow. At 100psi, rpm is irrelevant because, as per your own admission, 10psi/1000rpm is sufficient.

    And, that's only because you've got more than adequate FLOW. It's that flow when 'pushed' into the resistance (the engine) that creates a measureable pressure. No resistance, no pressure. No flow, no pressure. Lots of flow into a high resistance, lots of pressure. V=IR

    This is true to a degree. However, the Ferrari pump is overkill, and will produce volume (which when fed to a resistance creates pressure) far in excess of what is probably needed, even with very thin oil. You can try 0W0 if you like, and you will still hit the regulator at, say, 3000rpm. Or lower.

    Again, you will never get a linear pressure/rpm relationship with any weight oil, because the pump simply has too large of an output. Thinner oil will have an effect, but not enough. And that's precisely why a pressure regulator is needed to limit ultimate pressure. To use an electricity analogy, you're trying to power a light bulb with a nuclear reactor. Overkill.
     
  6. AEHaas

    AEHaas Formula 3

    May 9, 2003
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    Ali E. Haas
    4re gt4,

    Why are you not using 70 wt Redline engine oil in your car?

    aehaas
     
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  8. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
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    Why? What would be the point? As I've tried to explain (apparently w/o success), the F-pump has TONS of output.

    'Motor Honey' is used in worn out engines specifically to create some pressure. Mine's not worn out.

    I'm by no means saying that the pressure *should* be maxed out to the regulator all the time, but in practice it will be in a Ferrari because the pump has huge capacity.

    Put the thinnest oil you can find in your car and see. It's possible this could present problems at idle, who knows? But somewhere in the 2000-3000 range you will still be maxed out, regulator-wise.
     
  9. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,568
    Actually this is not true, I get a decidely linear relationship under all sorts of circumstances. At oil pressures under the point where the blow off valve operates, the oil pressure raises linearly with RPMs. When the oil is cold, the starting pressure is higher, and the point where the blow off valve take over is earlier in the RPM band, but the slope of the rise in pressure is exactly the same as when the car comes off the track with the oil stinking hot which is exactly the same as the slopw under normal street driving situations.

    The slope of the oil pressure buildup is the same between 20W50 oil and 10W40.
    The slope of the oil pressure buildup is the same between cold, street hot and track hot oils (independent of the oil formulation)
    The pressure of the blow off vavle is constant with only a minor varriance with respect to oil viscocity (formulation or heat)

    The pressure that is held by the blow off valve varies a little bit with oil viscocity with 20W50 at 105 PSI cruising on the street and 95 PSI using 10W40 stinking hot after a track session. This is simply due to the oil thinning out and flowing through the blow off valve faster as it thins.

    Looks pretty linear to this eye!
     
  10. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
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    Mitch: You missed my point entirely. It will be more or less linear UNTIL YOU REACH THE PRESET PRESSURE POINT IN THE REGULATOR. What I was trying to say is that it won't be linear from idle to max rpm, as aehaas seems to want. ie - It will never be 10psi/1000rpm all the way thru the rev range. The pump simply has too much output. You WILL bump into the regulator at some point, regardless of oil viscosity.
     
  11. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
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    OK, I guess I'll come clean as to why I *personally* will continue to use a heavier oil (15W50 summer, 10W40 or so winter) in my older car.

    A number of years ago I had a lengthy conversation with an engineer at GM's performance department. He did R&D for various NASCAR and Corvette racing projects.

    He explained that oil in a crank/rod bearing doesn't exist as a simple film. As one surface is sliding by another, the oil sort of 'rolls' between the two surfaces. It forms into microscopic rods, analogous to the needles in a roller bearing. The diameter of these 'oil rollers' was not dependant upon pressure, but viscosity. (And, of course, temperature's influence on viscosity.) Adequate pressure only assures that there will be an ample quantity of 'rollers', and that fresh oil comes in for cooling reasons. Again, the old 10psi/1000rpm was mentioned.

    He said that viscosity needs to be choosen such that the 'rods' are of the correct diameter, and fill up the clearance in the bearing. Conversely, the clearances could be designed to suit a particular lubricant. In many years gone past, we used to build small block Chevies with very large clearances. It's not considered proper now, but was the fad back then. You could put in 30W and HAVE PROPER PRESSURE AT ALL RPMS, but the motor wouldn't make it to the A-main. With 50W, it would last. Again, motors are being built now days with tighter clearances, so even racing engines will tend to use much thinner oil than we used to. Smaller clearances, smaller 'oil needle bearings'.

    Fast forward a number of years. As synthetics have less of a tendancy to thin with temp, a thinner synthetic may provide proper high temp 'oil roller' diameter.

    As my engine is 1975 vintage, I'm going with the assumption that clearances are such that Ferrari had a reason to originally specify a very thick oil. It's possible that this isn't true, but unless I disassemble and measure clearances, I have no way of knowing. Measurement of actual viscosity of hot synthetic oils, however, has me leaning toward thinning my oil a bit.
     
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  13. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,568
    Let me explain what I consider linear, and then we can see if we still disagree.

    I took the liberty of graphing up the data associated with my F355 engine under a variety of uses under two different mixtures of oil. This data is not all that accurate but let me use it to explaine what I see on my oil pressure guage.

    I present data for a cold engine at idle, a fully warm engine cruising down the interstate, and a hot engine on the cool down lap after a nice long run. I present data for 20W50 in red and for 10W40 in blue. I also graphed our old ruel of thumb friend 10 PSI per 1000 RPMs.

    Notice the slope of oil pressure rising with RPMs of all the oils under all the operating conditions have about the same slope.

    Notice that there is a large flat plateau for all operating conditions after the blow of valve opens.

    Finally notice that the break point between the sloping section and the flat section are nicely bunched.

    I consider this result to be linear under a broad definition of linear, under the narrow definition in algebra, it is not linear. Can we agree on this?

    If the break points were not so nicely bunched I would not consider these equations linear. This nice bunching seems to my eye to say, all this data is somehow correlated because all the surfaces are making an easy to recognize surface. Even though I don't yet know what variables join the equations.

    I will also point out that the oil pressure all tend to rise at twice the rule of thumb. I noticed this too in my Vette.
     
  14. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,568
    Rule of thumb is also valid for an engine with 100,000 miles on it after the bearings have sustained wear. There is more volume of oil flowing through an old engine than a new at equal oil pressure. But as long as the pump can push the volume, the blow off valve will be controlling pressure for the high performance end of the rev range.

    Rule of thumb is minimum pressure, so you want some margin above the rule of thumb.

    Added pressure only cost gas milage, insufficient pressure eats engines.
     
  15. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
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    Mitch: As I said above, pressure/rpm is linear UNTIL YOU BUMP INTO THE PRESSURE SETTING OF THE PUMP REGULATOR. By this I mean linear as in a straight line from idle to redline. It is a straight line until max pressure, then it flattens out. Mathematically, linear means that for an input (rpm), you get a proportional output (pressure). After bumping into the pump regulator limit, it's no longer linear, as additional input (rpm) doesn't produce a proportional output (no more pressure increase).

    This thread has split sort of into two separate subjects: 1) Rob's overpressure situation, why it's so, and what to do about it. 2) Can you keep adjusting oil viscosity until you get a perfectly linear 10psi/1000rpm w/o hitting a max value as set by a pressure regulator - as the preset value on early V8 cars is 90psi (give or take), which in theory is more than needed for the 7700rpm redline. Or for that matter, can you keep from hitting the pressure regulator at an abnormally low rpm? (ie - Can you keep the pressure/rpm response linear until a higher rpm value than we are seeing?) Basically:

    You'll never get a linear response from idle to redline because you'll reach the max pressure level of the regulator at some point. There will be a 'knee' in the curve where it will flatten out after a linear portion. Rob's original post was regarding a severe overpressure situation. I would strongly suspect that his pressure was linear all the way. The F-pump simply has too much volume to not reach a *properly set* pressure regulator. Regardless of oil viscosity. It's a positive displacement pump that, at higher rpm, simply puts out too much oil. And for an old racer, I'd rather have too much oil than not enough!
     
  16. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,568
    At this point I can't see how our two views ar different.

    At the level of algebra, this is true, as I said. But because all the data, as a whole, fits into a bigger picture, I say that there is a linear relationship connecting all of the individual oil pressure curves. In this sense it IS linear. And, as I said, in the algebraic sense it is not. <see below>

    I think the data contraindicates that you can achieve your goal. However, we don't know why the slope is the slope it is. If we knew we might be able to build a pump that did follow the rule of thumb relationship. What we get the first glimmer of is; that viscocity does not seem to be the variable that modulates the slope, just the verticle position.

    We don't disagree on what the individual curves look like, we only disagree on how we label the curves. In this sense whether its linear or not is moot. They still have the shape they have, and thats the important thing, the shape and not the label.

    An excellent observation; maybe the blow off valve is stuck or the piping after the blow off valve is clogged.

    Agreed.
     
  17. Wasco

    Wasco Formula Junior

    Dec 9, 2003
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    Randy
    Anybody seen low oil pressure due to sending unit, i.e. 45 - 50 lbs at 7k.
     
  18. 4re gt4

    4re gt4 Formula 3

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    Wasco: I had a sender fail a few months ago. At first, it was showing higher than normal pressure. Then after a few weeks, it read low. A month or so later, it showed zero pressure for perhaps the first 30 seconds.

    Low pressure reading is a common symptom of sender failure. BTW, you'll probably have to remove the filter adapter to replace the sender, so don't forget to order the gasket.
     
  19. rob lay

    rob lay Administrator
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    Just got word from Norwoods. New $4 spring installed and pressure is down to 100. Thanks everyone for the advice!

    I bet over 50% of the 328's out there are running 135-140 pressure and don't know there's a cheap quick way to bring it down.

    It didn't hurt my car before, my car has been running like that all 58k miles of it's life, but this makes it a little healthier. Kinda like improving your blood pressure. :)
     
  20. f355spider

    f355spider F1 World Champ
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    May 29, 2001
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    Thanks for the report back Rob. I agree, though they were supposed to be updated during the oil line recall, and the production change, seems a LOT of them slipped through....
     

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