OIL PRESSURE RELIEF VALVE SPRING

Your oil pressure guage is plumbed into the wrong place. The proper galley reading is to be read at the same place the original sender light is located. The hole going into the block just below and between your valve covers, directly above the oil pump.



You CANNOT get an accurate oil pressure reading from any of the ports that the original oil filter is plumbed into. The one you have your guage in, according to your post, is the one that guages the by-pass pressure.



I advised you once before to call the builder of your engine and get the lowdown on your oiling system modifications. I really don't think you are dealing with a "stock" Hudson oiling system.



Mark

Because John, the port you have your guage located in isn't subject to the same restriction the oil galley is, ie - the bearing clearances. The more restriction you have against the system, the more potential is preserved in the system. The less restriction, the less potential is contained (thats why worn out crank/cam bearings cause low oil pressures). The port you have your guage in is on the BACKSIDE of the by-pass piston and discharges into the oil pan, so it should be significantly less than the galley pressure due to the loss of potential - the lesser restriction. The only resistance to this flow of oil once it overcomes the spring is the clearance between the by-pass piston and the bore it sits in. Again, the tighter this fit, the higher pressure you will read at that port - but it DOES NOT indicate true galley pressure as its being delivered to the cam, main, and rod bearings. This has little to do with thermodynamics, its a hydraulic problem.



Unless Steve plugged the outlet into the oil pan, or placed a restrictive orifice in the passage back to the oil pan, it should in no way read the same pressure. I suspect your by-pass passages have been modified, or you have an extraordinarily good clearance between your by-pass piston and its bore.



A restriction in the return passage to the oil pan is highly likely as a method of flattening out your oil systems fluctuations due to the actuation of the by pass spring. If he did do that, he did you an enormous favor by eliminating the localized flow loss from the adjacent main bearing. When the by-pass spring allows the piston to open, it momentarily becomes the path of least resistance which decreases the amount of oil going through the main bearing 3rd from the front, consequently it reduces the flow to the 4th and 5th rod bearing compared to the rest of the engine.



Higher mathmatics in consideration, I really don't think you understand the system you are working with. I think you understand the drawings in your Hudson Service manual, but I don't believe that is the exact case with your engine. Its a Steve Farkaly 7x special, and he's the only one who knows what has been changed about your oiling system.



If you want to whip out the higher mathmatics, I'm game. In fact, I encourage it. I'm currently want to review my own oiling system's capacity and am taking measurements to apply a Bernoulli analysis of its adequacy. The Reynold's coefficients on the port passages are going to be impossible to get to any degree of accuracy, but the passage diameters are really what I'm after. Also, the amount of hp required to turn the pump in a range of pressures given the viscosity of the oil I intend to use.



All the science in the world isn't going to change the basic mechanical fact, that you are measuring oil pressure in the wrong place - get over it.



Mark Hudson

Twin-H, that is a very FINE looking powerplant you have there! Is that a Clifford head I see resting beneath those shiny air cleaners? Beautiful.



Your oil pump seems quite busy. The steel lines coming from your oil pump forward, do those by chance go to an oil cooler? I'm going to assume the AN fittings go to the remote oil filter.



With these remote filters, you still need to be aware of pressure differences associated with which side your guage is on. If you have your guage fitted in the supply side of the filter coming from the oil pump, your pressure is going to be higher than that of the actual oil galley due to the resistance of the filter element. If the guage is located between the filter exit and the oil galley (In Twin-H's picture, that would be the braided line with the red fitting going into the block between the valve covers) then you are reading the actual galley pressure being delivered to the mains and cam bearings.



From what I can tell of the pictures, the guage is located in the same by-pass port that has been discussed here in huge detail. The fluctuations of the guage will never ever go away, regardless of oil/filter, in this port. The range of pressures in the fluctuation sweep will change a bit, but the needle will still swing and get worse as the oil warms up and reaches its lowest viscosity.



Twin-H, looking at your driver's side - I can see the guage and sender switch in the port above the spring retaining nut for the by-pass. I think I also see another sender switch in the lower port, just below the by-pass. The upper position is actually not a bad place for the sender. If its calibrated to ground at 13 psi, that should be just fine for a new engine with a good fit between the by-pass piston and its bore. If an engine can't maintain 13 psi here at operating speeds, it would be a good early indicator that something is getting out of tolerance. On an older engine with some wear, be prepared to watch your idiot light dimly flicker at idle once it warms up. However, if you have a pressure guage at the right location - you'll know what the steady galley pressure is regardless of the dimly flickering idiot light.



Its been my experiance that going from 10/30 oil to 20/50, nets you about a 7 psi change in oil pressure as measured from the proper location in the circuitry. The thermodynamic application of a oil in a system is more a function of the ability to absorb and transfer heat, both from its own internal coefficient of friction and the work being imparted to it, as well as its ability to absorb and transfer heat from the other systems it comes in contact with. Oil does change characteristics as its temperature changes. These changes are what your oil's rating describes and its a measure of its viscosity at a certain temperature.



This next part is for John, because I'm trying to understand how this all hinges on thermodynamics alone. I'm looking to understand this perspective.



In a simply hydraulic system, the heat changes are due to friction the fluid encounters; its inherent friction due to shear, the friction imparted by its passing through a conduit, and the motive application of force in order to accomplish a given amount of work. Internal combustion engines also add heat generated by the combustion itself and the friction of its motion. What this heat does, and John noted, is change the viscosity of the lubricant.



The relationship viscosity has with a Bernoulli analysis is one of Friction. The more viscous the liquid is, the greater its internal friction is and is why its "thicker" to the feel. Viscosity is a determining factor in the Reynolds number, that ultimately determnes the frictional head. So viscosity does have a huge bearing on a Bernoulli based analysis of fluid mechanics. The variable that exists in the case of lubricants is the change in viscosity due to heat. So, thermodynamics certainly is an element as it relates to the lubricant, but only within the range of heats generated by the system itself and those imparted to the lubricant by its surroundings. As the viscosity lowers with heat, so does the frictional loss to the system. The work required to move the fluid lowers, and the pressure drops to reflect that change in viscosity - if all other variables in the system remain constant.



The way I understand the role of thermodynamics and the effectiveness of a lubricant is its ability to absorb heat and remain viscous enough to form a hydraulic layer between bearing surfaces. The amount of tolerance between bearing surfaces really determines the desirable viscosity range of the oil. You have to know the working heats associated with your engines conditions and match the viscosity at working temp to what is needed to maintain that hydraulic layer. Here is where manufacturer's guidelines are important - they figured that out already based upon empiracal trials. If your tolerances are closer than normal, you can get away with running a lower viscosity oil - the converse is true also.



This is why a newer engine is broken in with a lower viscosity lubricant. The tolerances are closer and the available clearance for a hydraulic layer is "thinner" between bearing surfaces. This allows a certain amount of "lapping" because surfaces are close enough to influence each other. As an engine wears and "laps" those few .0001" between surfaces, then a more viscous oil needs to be used to take up the slack in the allowable space needed to maintain the hydraulic layer between them.



I understand where thermodynamics come into play. But what I don't understand is that your oil pressures are outside the range of thermodynamic influence given the lubricants you are using? If you change the viscosity of the oil, you are going to change the pressure a small amount relative to the difference in what you want to run and what it is running. The solution then seems one of fluid mechanics rather than a general themodynamic problem. I do not understand how a change in viscosity or themodynamic property of your oil is going to drop your pressures 20 psi at idle, without lowering the viscosity to a point where you ultimately destroy your engine by compromising the ability to sustain a hydraulic layer. As I see it, you'll have a huge thermodynamic problem then - when your bearings begin to demonstrate properties of viscosity.



Mark Hudson

Think I need two tylenol pills. My brain's a spinnen.



Randy

I'm like your idea better but a bit to fancy for me. Look guys--keep it simple. 1. You are not going to wear your bearings out at 50 lbs of pressure. Know what your main bearing and rod bearing clearances are relative to selecting the weight of oil you use. I doubt there is a tinkers dam worth of difference between the 5-30 & 10-30 when hot. After knowing what your clearances are and the side clearance is select your oil. I always run .003 on my mains &.002 on my rods running 20-50 valvoline in my race car. Yes, I run .025 side clearance. I want the oil in and out as fast as possible to cool. I look at the back of the bearings to determine how hot they are getting. With the extra side clearance, they will run cooler. The oil pump will flow plenty of volume.

Sorry, I don't know much about your laws.



Forrest Gump