Thread: oil pressure

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whats up guys?
first time post. i have a 77 chevy el camino. 350 that im trying to build up for more power. already put in new cam(edelbrock performer), intake(edelbrock performer), headers(headmen), flowmaster cat back kit, new distributer, and all gaskets and hoses. ive been having a problem keeping oil pressure up. during idle i get almost no pressure, as soon as i put some gas to it , it goes up to almost 35 psi. What might be the problem ?

I'm guessing either cam bearings or maybe a piece of trash in the reilf valve in the oil pump or idle too low.

Kodiak

the bearings were in good shape when i put the new cam. ill check the relief valve...maybe the valves need adjusting ?

Here would be my assumption.

If your pressure was higher before the cam change than it tells us that during the cam swap you gouged out the bearings and caused a bleed out of oil in the cam journals.

If the pressure was unknown, or if the pressure was similar prior to the cam change than it tells me this: Your main/rod/cam bearings are out of tolerance and therefor bleeding off oil pressure and taking with it the integrity of the entire oiling system.

I doubt its a forign object in a relief valve, its just way...way...not likely.

I would say your going to be putting some bearings in this thing if you want to get the pressures up, or can crutch the worn bearings by applying the devels advocate...a high vol/pres oil pump.

Why do I call it the devels advocate? Well, it takes more power to turn a higher vol or a higher pressure pump, and it creates more latent heat in the oil, so your bearings get less effective cooling from the now hotter oil.

Also, as MME Racing preaches, the worn bearings are bleeding oil, the oil is being swept up in the windage created by the rotating assembly, and this in turn is airating the oil. Once the oil gets contaminated with this air and gets forced into the bearings you have a second bad thing, the oil got hot in that high vol/pres pump, and it cooled less, and now with air bubbles mixed in the oil it has the ability to cool even less again!

This is why even in my 8000-8500 RPM engine I do not run a high vol/pres pump, and why I do run a good windage tray. I keep the oil that I have clean and cool, and ready to do the job.

Before I ever read Larry 0071's post, I was thinking exactly what he said in his very first statment. You proberly scratched the cam bearings when you installed the new cam. It sounds like this is not a fresh rebuild on this motor and this is not an easy fix. How cold is it where You are ? You could increase the viscosity of your oil( go to a heavier weight) and it may help some. With the motor you have you're not going to be turning too may RPM's so I think Your application and Larry"s are two different things. In your case I think putting in a high volume pump might help. It doesn't take a lot of oil pressure for that motor at idle,So If You have 30 or so pounds,say at 3000 rpm's on the highway you should be OK until You're ready to do that total engine job. JUST MY OPINION, BUT I've been there. Did the same thing years ago and I ran the fool out of it with no problems.Don't know what your results will be.Good luck!

Well, I do actually understand how and why oil pressures are regulated inside of an engine, I am sure your not suggesting that I didn't, rather your giving your opinion that is contrary to mine. That is good, its always good to dig in and see why we have the ideas that we do :]

High oil pressure. I dont really higher than is needed. About 10 lbs per thousand RPM's is a good baseline for street use as well as most race applications. If your pushing 60-80 lbs of oil thru an engine at say.....2800 RPM cruise, would you say this is better or less desirable than say 35-45 lbs? I would rather have the 35-45.

Here are some things to think about:
An engine using a High Volumne oil pump, that has stock clearances in it will cause the oil to take the path of least resistance, which in many cases is the upper cylinder heads, if not restricted. When you restrict the oil to the top end, and use factory tight clearances, you cause the HV pump to build more pressure.

In my opinion, you are starting to turn your oil pump into a hydraulic pump, rather than just being the supply pump it was designed to be. Remember, without resistance to the oil pump, you will have 0 oil pressure. "Resistance" is the key word. It is all a delicate balancing act. Your oil pressure is a combination, and the sum of all your clearances in your motor.

It has been suggested over the years by the likes of Roush, Smokey, Jenkins etc that more than 10# per thousand washes the bearings and can actually allow metal to metal contact by destroying the hydrodynamic wedge that supports your bearings.

High pressure can "float" the bearings that usually leads to spinning a bearing. It also causes high oil temp as well as airation and will wear out the distributer/cam gear quickly and can cause broken distributor gear drive pins. Try for 10 lbs pressure per 1000 engine rpms.

Your concerns are not new ones. This question has been, and is still being asked by a lot of people. No one that I know, or ever heard of, has actually tested the oiling systems on engines to get the answers and documented it. It's all a big ball of opinions. Not every engine's requirements for oil are the same.

A warmed up street motor has less requirements than a high performance race motor. The bearing loads can be calculated on the rods and mains.

I've always been a little leary of the HV pumps in a street motor, with street clearances. They can be too much! It's how they are used, Don't forget why they were made in the first place....for a worn out engine to help bring the pressure back up.

The oiling system is a balancing game. It's a balance of volume, and resistance, both of which produces pressure. Somewhere, someone might know how much oil is required in volume delivery at the bearings and friction surfaces to maintain sufficient hydrodynamic and boundry oil layer. I don't know him!

First off, we know that the job of an oiling system on an internal combustion engine is to reduce friction, remove heat, and maintain a hydrodynamic and boundry layer of oil film to prevent contact of the bearing surfaces. The required volume of oil necessary has to do with several things; rpm's; clearances; bearing surface area; and bearing load. All that is required is enough oil be present to form a hydrodynamic film to keep the rod and main bearings from contacting each other.

How that is accomplished is... think of the oil film layer as a big wave with a surfer riding and sliding on it. The wave keeps the surfer from coming into contact with the ocean bottom. Boundry oil layers are similiar but they are more friction prone. This is the lubrication on the cam lifters and lobes, rocker arms...the piston's in the bore, etc.

The science of all this is extensive, and their isn't enough room or time for it here. I hope this explains SOME of it. It doesn't take massive amounts of oil to create the hydrodynamic layer. As a matter of fact if you start using large clearances, your oil volume requirements will increase. How much clearances? Another big guessing game.

Everyone has an opinion. For the street, I think that the high side of factory shop tolerances is perfect for high performance street engines. That is usually about .0025 thousandths, on the mains and rods. On a street motor, I don't think it is necessary to have different clearances on the rods and mains. That's what 3/4 shell main bearings are for. I have seen many posters in another forum report that they are using larger main bearing clearances, and smaller rod bearing clearances. This is not correct...it's backwards. A fluid under pressure will take the path of least resistance. That means if the main clearances are larger that the rods, the rods will get less oil. Usually larger rod bearing clearances are used in aluminum rods for racing motors, because of their heat and growth sensitivities. More clearances in the rods on even steel rods are used generally for cooling purposes, because the piston transfers heat from the combustion chamber down through the rod and to the rod bearing.

Also the rod journals scribe an arc and because of centrifical force they throw the oil out of the rod journals (This will cause the rod bearings to fail if not enough oil is supplied) and if you have too much rod clearance and too much oil system volume... the rings can't handle the extra oil and it goes to the combustion chamber! Hence, the need for more oil at the rods than the mains, but keep the rod side clearance in check to minimize centrifical oil losses. The mains do not have that problem. Their problem is how to supply oil to other bearing surfaces in enough quanity, and still have enough to maintain their hydrodynamic layer requirements.

A "High Pressure" oil pump, might very well be the one to use in some applications, but...... I've heard many a person complain about pumping all the oil up into the heads and the pump sucked air. You only have so many places in the upper end measured in square inches for oil to return and complete the cycle. This very well could just be a big oil curtain pouring down on the crank and rods... frothing and slowing everything down.

Those larger rotors pumping the oil require more power be transfered through the pump shaft and timing chain. It'd be interesting to see what that did torsionally to the cam and timing!!!

These are some of the thoughts I have as to why I am not a fan of high vol/pres pumps. If clearances are big, go with a high vol as a crutch, but leave the high pressure pump in the store. I would rather see you replace the bearings with new stock bearings and I am sure that you will pick up some of the worn dimension in the journals and this will for sure give you back some of the "lost" oil pressure.

Sorry this is so long. I hope no one is offended. As usual, this is JMO.

It "can" be done, but my god, what a cheesy way to do something. If your really going for a proprietary oiling system and you get down to last part, restricting the top end...and you go to the hobby store and get pipe cleaners that may come apart and do who knows what to who knows what........not me buddy!...lol!

My engine is restricted, but just about 98% of the engines out there are more than fine with factory oiling, assuming the tolerances are right and ...and this is the big one that most folks ignore...the LIFTER BORES are not oversized from wear!. Yes, the lifter bores are a common source of lost oil pressure! If you have a 200K mile engine the chances are that the lifter bores are bleeding oil like a stuck pig. Its lowering your pressure, increasing airation of the oil, and in turn can cause a bearing to spin beacause we all know that oil lubes and cools, but air bubles dont lube to well, nor do they cool to well! So, as I was boring my lifter bores so that they actually point at the cam centerline (Most do not, they are close, but no cigar...) and we had to bush the bores back down to size why not use the bushing as a orifice to regulate the oil flow to the lifter/pushrod. I mean heck, I have roller cam bearings, solid roller lifters, jesel shaft rockers...what do I need oil for. My engine only runs 30 seconds at a time, its not like I need long term oiling for street use. Each time I start it, I put the drill to it and lube it, than it is started.

Back to the point, if your doing a nice street engine, and your doing it right you should not need to restrict the top end, you should not need high volume or high pressure pumps. Build it as designed and it should be fine. The 383 Chevy I just did is 60 lbs cold, 25 lbs hot and 55 lbs at cruise...all with a total stock replacement 19 dollar oil pump!

this is the first time ive ever seen anybody fix their motor with an oil pump when the pump wont broke. i agree with most of the discussion about what a pump does except when you start talking about somehow making the pump perform a miracle on a motor with some kind of oiling problem. you'll giving the pump way to much responsibility. if you clearances are not right then the pump ant gonna fix it. the pump has to be with in a certain range but that's about it. if the pump is not worn out, sucking air, or the relief valve stuck wide open then i don't see much else you can do with the pump. ive all ways used a HIGH VOLUME pump and stayed away from the hp pumps and i believe i can honestly say oil pumps never caused me a lot of problems. Clearances,clearances,clearances is what it all about. get your clearances right, get the oil back in the pan, with a good oil and the pump will do what it supposed to. A good discussion but the pump ant gonna fix his problems, he needs to do what denny says, find the leak. JMO

0 at idle and almost 35 at cruise....you need to put bearings in it. Period. The shame is that on most things you have to yank the engine to get room to get the crank out, pain in the butt, but I hope you have a garage and a engine lift. Sorry, I know its not what anyone wants to hear. Just look at it this way, your going to be heading off a major problem, such as a spun bearing.

This is all very entertaining, but kind of a waste of time except for watching some of you "duke it out". Since the originator didn't give enough information to do a proper analysis all we've been able to do so far is some wild a$$ guessing.

First, oil pressure in and of itself don't lubricate squat. It is meaningless without some points of reference. Oil lubricates bearings, not pressure. Oil in motion creates the hydrodynamic film. Hydrodynamic films exist all the time in non pressure fed systems. Just ask anyone with an old Chev, Hudson, etc with "splash" lubrication systems as well as countless industrial applications. Heck, wear some new leather shoes out on a slick, water covered concrete surface, you'll get an empirical lesson in hydrodynamics..................without benefit of a pump. If you plugged the oil pump outlet three inches down stream and took a pressure reading on that section of line you'd get a pressure reading, but the oil wouldn't be getting to the bearings. Right now someone is saying that isn't plausible. Well, the three inches may be off, but it's been done by some installing a bypass valve backward or hooking up a remote oil filter incorrectly. Couldn't understand why the engine seized because they had pressure! Give me oil flow before oil pressure any day. The value of the pressure reading is only meaningful if it deviates from the norm with no other changes having been made, or changes in the environmental conditions.

So, while some of the guesses above may be correct, there are other possibilities. Does he have a crappy filter that is restricting oil flow at low rpm, and only registers a reading when the pump is pushing harder (dumping the bypass in the filter)at higher rpm's? Is he using too thick of an oil, different than what was in there when he last remembers seeing the pressure? Was the oil pressure reading similar to this before he diddled with the engine, but he didn't notice it until he became forcused on the gauge because of the work done? Are the ambient conditions the same (temp both ambient and engine, rpm, etc.) as when he saw the numbers he remembers? Does this 0 to 35 psi stay the same whether the engine is cold start or warmed? There's more, but until he starts to check off all the variables this just continues to be a guessing game.

Hey its too much clearance on your crank ie mains I have the same problem , went through new guage new oil pump etc . prozac lol a couple off beers and aprox 30,000 miles later it still hauls ass. as long as the pressure does go up with the rpms and you are not running Nos you will prob be OK