Hot Rods "New" small block oil pressure

My answer to the original question is 1. get a second oil pressure gauge. 2. If you don't see more oil pressure, something wrong. 20-45 is the normal oil pressure for a small block in good shape IMO.

 

Jim Forbes is correct, of course
Now, if that engine was run on a Dyno, then there is no need to run it for 20 minutes for the cam. That's done
If a plug were missing the operator would have been concerned.
Your engine is fine. Run it

 

Squirrel, Have you ever seen a bleeder on a bourdon tube?

 

SAE paper on sliding bearing failure analysis, I will just post the lubrication section, and leave out the stuff on calculating the Sommerfeld number, anyone that wants to go deeper can google that...

This should REALLY piss off the rod-abilly types...

 

SAE paper on slidingbearing failure analysis, I will just post the lubricationsection, and leave out the stuff on calculatingthe Sommerfeld number,anyone thatwants to go deeper cangoogle that...
Damn, now I gotta buy a calculator?
Life was so much easier with straight 30 weight and idiot lights.

 

This thread is turning into a which is better, Ford or Chevy. If the engine has already been run then put the accessories on, fill up the radiator and run it for awhile then check for leaks. Old school that got us by for a long time is 10 pounds of oil pressure for every 1000 RPM. I have raced SBCs that made enough power to twist crankshafts that only had 30-40 pounds of pressure, it all depends on bearing clearance and how you set it up.

 

You did not mention the engine size. Had a similar problem with a 283. Someone had converted to a spin on filter and did it wrong and cost the customer an engine.

 

Only if you are really reading between the lines...I would think of it more as which is "better", and for what, "large" journal diameters or "small", I know which I prefer, from an oiling standpoint anyway. Honestly, I am being conservative running 47 psi @ 7000, comp eliminator guys probably laugh when they read that. Hell, I'm not even pushing the envelope. 10 psi per 1000 rpm in a sbc is flat earther stuff...

 

Mostly posted that in support of Blues4U's post, which is pretty much right, reading the SAE paper I posted will make it clearer.

 

There you go getting all NASA on us again....

 

So the old hydraulic vehicle hoists that used air to compress the fluid and raise a car shouldn't work? I'm glad they didn't know that as I used them quite often!

From Wiki

"Pascal's principle applies to all fluids, whether gases or liquids. A typical application of Pascal's principle for gases and liquids is the automobile lift seen in many service stations (the hydraulic jack). Increased air pressure produced by an air compressor is transmitted through the air to the surface of oil in an underground reservoir. The oil, in turn, transmits the pressure to a piston, which lifts the automobile. The relatively low pressure that exerts the lifting force against the piston is about the same as the air pressure in automobile tires. Hydraulics is employed by modern devices ranging from very small to enormous. For example, there are hydraulic pistons in almost all construction machines where heavy loads are involved."

Air in the line will cause a slight delay in the time it takes to show a pressure change but it would be milliseconds.

 

That's a great paper, and explains things much better than I could've in a post. The reason I even mentioned it was that the OP seemed worried that he had maybe damaged his engine running it with only 10 psi of oil pressure, even though several people posted that there was reason to be worried. Trying to give him some assurance that it's OK, and pass along a little info at the same time. That is the point of these discussions, isn't it? Thanks George.

 

50 PSI is 50PSI air bubbles or No air bubbles..........

The only thing I found when I was young and messing around with Fu&*ing Junk Gauges with small diameter plastic line was....... a far greater reaction time to pressure change than a larger diameter line.
The small diameter line took much longer to bleed off the high pressure when going to a lower pressure. (Experts chime in)
You could lose an oil pump drive and be staring at the gauge and not see the failure in time to save the engine.

If this SBC has this low of oil pressure with COLD OIL at idle something is not right... end of discussion.

I would already have it on an engine stand taking it a part to fix it.
Good Luck with getting this sorted out and I hope it is an easy fix for you.

 

yea, actually knowing a little about how this shit actually works is "unfair". Or maybe its not the knowing, its sharing the knowledge with others thats the problem.
I hang around on another forum, I am frequently mystified by some of the conversations on there, but instead of bitching about it, I try to up my game, so I can learn from them, and at least sorta follow what they are talking about.

 

@squirrel @stimpy
My thought exactly. You can't bleed the bourdon tube, so there's not a gauge in the world that can be accurate if what some are saying is true.

A brake master cylinder only has a limited amount of liquid that it can move on a stroke of the piston, so if there is air in the lines then you will not be able to build the pressure you need due to the compressibility of the air in the lines. An oil pump does not have this limitation, so once the air in the line is compressed to equal the oil pressure, the gauge will read the correct pressure. And I'm not concerned about a 0.5 to 1 second delay in my oil pressure gauge reading the correct pressure.

 

Yup, this is the reason for using the large metal line, its not the steady state reading, its about how quick the gauge reacts (one way or the other) when the shit hits the fan, which is what I thought was the whole purpose of running an oil pressure gauge in the first place... But then, I guess a lot of guys run this stuff for looks...
I am with-holding judgement on the actual reading, if the engine was broken in on the dyno as the OP says, I would be contacting the engine builder and getting his feedback before I did anything else.

 

When the shit hits the fan, a better solution is a pressure sensor that will shut the engine down with no intervention by the driver. Usually my eyes are on the road or the track, not staring at an oil pressure gauge.

 

Yep, it's even harder to keep an eye on the gauges on the common Deuce style dash with the gauges mounted in the center of the panel instead of in front of the driver.

 

On a daily driver maybe...... an illed timed engine shut down could be a very bad thing on a Race Track (Road Course) at this point a Engine sacrifice would be better than losing the whole car to a wreck.
When I drove my FED after the launch the only Gauge I cared about was the Oil Pressure.
You would be amazed at what goes on with Oil pressure in a Quick Fast Straight Squirt and a very quick Stop.

 

Before you pull thing apart, I'd get a good quality gauge, or have a mechanic come by and do another pressure test. 10 lbs at idle is likely enough, but I wouldn't be happy with it. I just fired my 350 up on a dyno last week and it has about 25 lbs at idle and 65 lb at 5500. What would really bother me is being able to turn the engine over by grabbing the damper with the plugs still in.....doesn't sound right to me. I have to pull my plugs to be able to turn it over with a breaker bar to the damper bolt. Put a tach on it and see what the pressure goes to at each 1000 RPM. Chevy used to say 10 lbs for every 1000 RPM. (give or take). If you do end up pulling the pan, I'd be tempted to plastigauge the mains, could be a little too much clearance. Good luck.

 

well 10 pri for every 1000 puts me dead on. just doesn't seem right. my DIPPER stove bolt went to almost as high as it would driving down the road when idling could. Idle hot: 7psi. 50mph: 14psi. Idle Cold: 10psi

So i talked to the guy i got it from. Did not ask for dyno report - will call back if i want it but i don't have a reason yet not to take him at his word i guess. He said when it was being tested there was an issue that involved putting a new spring in the oil pump and after that it ran at 40 psi around 3000 rpm. He said he wouldn't be content with it at 10psi and suggested I swap the pump.

For now I think I am going to keep working on other tasks. when the car is all put back together and there is a cooling system (and charging system if I can run 30 minutes on a battery) I will run it for a while and get it tuned, get the coolant flowing and such, and se how my pressure is after it runs for a bit. I will also rev it up more and see what kind of pressure it makes around cruising speed. If i am not satisfied then, i'll change the pump. If that doesn't solve the issue, I'm out of luck and in a real bad spot because my money tree isn't blooming and I have a family to take care of

 

I cannot turn the thing what so ever without the plugs out and even then its a 12' rachet

and thanks!

 

In an earlier post, it was said you could turn the engine over, with plugs in, and both hands on the balancer.
Squirrel and others commented on that being abnormal, for a new rebuild.
Did the seller provide you with a list of what he replaced, as part of his rebuild?
That info could be critical to isolating your oil pressure concern.

 

Even if the seller doesn't have the dyno sheets, the dyno shop likely has it in their computer records. Any chance of getting hold of that? It should give you the oil pressure throughout the test, as well as HP etc. I know you can read the blow by on the dyno instruments, but not sure if they show up on the printout. I don't think mine shows that.

 

I prefer whiskey to bourdon. How much is a good oil pressure gauge? Maybe $40?

 

I have also already suggested that he needs to talk to the engine builder, but for whatever reason, he doesn't seem to want to do that.

 

this was in reference to an old wore out 235. The new 350 he's working on now, he can't turn over by hand.

 

The only way you are going to sleep well at night is to drop the pan and see what's what in there. I would pull a couple of bearings (both main and rod) and see how they look and how they check out clearance wise. If all looks good, buy a good Melling high volume oil pump and an ARP oil pump driveshaft, and button it up. Put some 20-50 oil in it and see how it is now.
I would not feel good about that low of oil pressure, I would be constantly looking at the gauge and worrying. The story the engine guy told you about "having a pump problem "when they dyno'd it, sort of makes me very suspicious.

The work I outlined above is all of an hours work, and it will tell you volumes about what the inside of that motor really looks like and if there is some problem. Oh, and I would also check out the oil pump pickup to make sure the screen is clean and that the screen is close to the bottom of the pan.

You really need to get inside there and take a look IMO.

Don

 

My guess is very few guy on here are aware that oil pumps have an internal by-pass, or at least pause to consider the ramifications of that. This means that when the pressure on the outlet side of the pump goes above the bypass spring pressure, the pump re-cycles the excess oil internally.
So when you put a high-volume pump on an engine that doesnt need a high-volume pump, you exceed the pressure of the by-pass spring at a lower rpm than you do with the std. volume pump, and start re-cycling a greater volume of oil inside the pump at a lower rpm. An excellent way to increase the oil temp considerably before it even gets to the bearings, not really what you want, considering that absorbing heat from the journal/bearing interface and valvetrain is one of the oils primary jobs...

 

Check clearance on pan to pick up if you pull it down I have seen low oil pressure due to a pan being smashed or clearances too close to the pick up screen. I agree with squirrel I think the time to compress the air and the fluctuations in the gauge would be so minute you would never notice them. I have had plastic ,metal, big and small lines I could never tell any difference despite what all your papers say. TSTM. Also try 3 different gauges and they will each give you 3 different readings.