trying to figure out what is happeing. 1000 mile rebuild on a 68 corvette I purchased, 327 w/350 HP. no further contact with previous owner. when started, oil pressure pegs at 70 psi, ran 10w40 for two oil change cycles, pressure always stayed at 70. very disconcerting. recently changed to 10w30. When engine warms up to 190 deg the oil pressure drops to 35psi at idle. Never saw this before. Moment I rev the engine the pressure soars to 70psi. verified that engine has comp aluminium roller rocker arms on flat tappet hydralic lifters and cam. engine is suppose to be a Hiperf L79. I read that when using the comp aluminium rocker arms that lots of oil flow is important. I also read that the 327/350hp hiperf has a hiperf oil pump in it, but I can find no info. I have no other history on the car but the word is that the person who did the engine was competent and experienced. the 70 psi scares me because I have read about excessive wear and strain on the the distributor drive gear from pushing the high pressure. So I am wondering, is the 70psi all the time except warm idle too much? Is the Distributor gear in danger? should I change the pump? Is it the pump? Am I getting worked up over nothing ? Any advice would be appreciated. regards, Atlanta

 

Here are basically the four pumps "stats" from Mellings for example:

Std pressure / std volume
Std press / HI Vol
HI press / std Vol.
Hi press / HI Vol

What makes these pumps different? As far as volume goes, it is determined by the size (length) of the gears inside the pump casing. HI VOL have 25% longer gears.
As far as the pressure differential, that is determined by the strength of the spring inside the pump. These springs can be ordered in an array of different pressure setting and each spring is color coded for ID ing. Summit sells the springs by color / pressure in lbs.

Perhaps the engine builder installed an above std pressure spring. These can be changed out in a bench vise by removing a drift pin. Of course, the pan & pump will need to be removed, new gasket, might be able to drain the oil into a clean container, and reuse.

Great time to switch to Oil Pan Stud Kit and verify the pickup screen depth & angle is exactly where you want it.

Myself, I would let it go. Keep the pump. There are more people complaining of low oil pressure than too high. Consider yourself lucky.
I would not worry about the distributor gear; they are very tough. It's not like you are shoving 50W through it while turning six grand.
To have that good of oil pressure means the bearing are very happy.

And I would not worry about the aluminum rocker arms getting enough lube. Friction needs lots of oil. Stamped steel rockers have lots of friction, at the rocker ball and at the valve tip. The whole idea of roller rockers is to reduce friction and thereby need less oil.
It's been said for decades that the SBC has W-A-A-Y-Y- too much oil topside. And that always posed the notorious Valve Cover leak. An old trick was to reduce oil in the passage ways for the lifters.

Don't worry about oil pressure. After several more miles and the switch to 10W-30, I believe things will settle down.

 

More than likely has a high volume pump in it. You might verify pressure with a mechanical gauge....but i wouldn't worry about it. For reference it's best if the pump isn't "peaked out" and bypassing at max pressure all the time. The issue is the oil can get foamy and air bubbles in it. Best if it goes up to 50-60 or whatever when cruising and then hits 70 or peak when wide open with some RPM. Does it go higher than 70?

Your gear will be fine. I've been running that sort of oil pressure on everything I've ever owned and never worn a gear out yet.

JIM

 

High oil pressure is fine . Low oil pressure is not. I never had issues running 15w50 and having 70 psi all day long on my big block. On my small blocks they would drop at idle..... i switched to 10-30 on my last rebuild and a bearing came apart at 500 miles... never an issue before. May have been a coincidence, but i will never use 10/30 again. Too many variables in todays parts and oil quality compared to 50 years ago

You want 10psi for every 1000 rpm is the old rule of thumb, more is better

 

Setup a second oil pressure gauge under the hood and verify......the port is easy to access, put a tee on it and compare gauges. If you verify, pull the pan and look for the HV pump......replace with a standard volume pump. There is a lot of controversy about this but know that if your bearing clearances are .002 or better on a small block, an STD pump will not have 70psi no matter what you do.....unless you are class racing, the HV pump just moves too much oil......and yes they make both Std. and Hi-Pressure HV pumps.....the only differance being the blow off spring as Jim stated......but the extra volume spikes the pressure faster and even if it blows off at say 65psi.....it isn't good to run like that also as Jim stated......These HV pumps are dependent on .003 or better clearance to operate properly and still at that clearance move too much oil on the street......
You don't have to worry about the distributor gear if you are like most of us and just pleasure cruise but you will see abnormal wear on the gear after 10,000+ miles...depending on the gear.....the difference between the two pump at 6000rpm is 7 horsepower.....and that's a lot. We tested it years ago......on a 383 Dart block Little M.....there may have been dyno percentage error, but you can count on at least 4-5hp.....still a lot.
So....either one or both are happening.....your clearances are too tight or it has a HV pump..........but the way your pressure spikes real fast leans me to say both.
You would be surprised how many engines that do not need a HV pump have them and how many Pro built engine do not have one.......
I like 25psi at idle and 65psi at 6000rpm.....and generally when you have this...the needle sweeps nice and quickly with the tach......
You could even Plastigage a couple of rods and mains while the pan is off....but that is up to you. Make sure you have the IS55 shaft with steel collar and I always like a stud to hold the pump on.....still a bargain at $6.....
If you put a std. pump on it......check pickup depth to the pan bottom (5/8"-3/4") and have the pickup brazed to the pump all the way around.......this will eliminate any chance of aeriation.....

Jebby

 

I made the stupid mistake of the using the Melling High pressure/High Volume pump on my 1968's 427. It would peg the oil pressure gauge until the engine was fully warmed up and then drop into the working zone of the gauge after the oil was fully warmed up. I was told that on Chevrolet Big blocks that you do not want the high pressure oil pumps due to excessive pressure on the rear main bearing causing premature wear on the engine block. The engine block has screens in it to catch any parts from the roller rockers and they slow down the cold oil a bit. I took the car to a trusted mechanic who replaced the pump with a standard volume/Standard pressure oil pump and the pressure numbers are back where they should be. They did this over 20 years ago and the engine doesn't drip any oil which is a real plus.

Being a private pilot I learned to sit patiently until I saw movement on the oil temperature gauge before trying to move or take off. Today I do the same thing on my Corvette, I will start it and let it warm up a bit before driving it. I have my wife and kids trained to start their engines and let them idle for at least a full 60 seconds before putting a load on the engine. It is always better to have the oil flowing throughout the engine before loading it up.

If you don't trust/believe your oil pressure gauge readings then hook an external oil pressure gauge temporarily and compare the readings. It never hurts to verify that the gauge is accurate. My 55 year old oil pressure gauge read 10-15 pounds of oil pressure when the engine was shut off, I don't know how to reset it if possible, I do know after comparing that the reading after the engine is running are "close". Kind of like my Ammeter showing 10+ amps charging when the engine is off. I bought a kit with an external Oil pressure gauge and a lot of fittings to allow me to verify oil pressure in virtually any engine with pressurized oil.

 

I have the standard GM LT-1 pump, been on there for almost 30 years. 10w30 oil, (Diesel), gauge is maxed at 70 lbs cold, hot is 65 lbs highway cruise and about 35 at idle, 750-800 rpm. No issues so far.

 

That will spin the Hobbs on a cold winter day....LOL but I get it....

​​​​​​​60

 

I’m glad to hear this. I’ve only owned my 72 LT-1 for around nine years but what you describe above is exactly what I experience in my car using the same weight oil. I’ve always wondered if it was “normal“.

 

The 427 small block in my '79 has a standard volume pump, but I put a higher pressure spring in it when I assembled the engine. If I can believe the factory gauge, I get about 70 lbs. at startup. When it's warm it's about 35 lbs. at idle and maxes out at about 65. Been running like that for about ten years with no problems. I pull the distributor out every winter for a look and no sign of unusual wear of the drive gear.

 

Same behavior on my 5,000 mile 350/290 GM crate motor, it has p/n 93442037 high volume oil pump.

 

Related question:
My pressure on my original '69 small block tends to also run high per the dash gauge (around 70 cold and ~40-40 warm idle, and maxes out at 70+ when hot and revved). 10W-30.

Never thought much of it until I recently have been chasing an oil pan leak around the rear seal to the block.
I've swapped out 3 new Fel-Pro 1-piece seals with adequate beads of Great Stuff on both the front and rear "smiles" and in the corners.
Still getting a slight drip (maybe 3 or 4 drops on the floor) after warm up and shut-down, and after sitting still for a while. After the few drips, it stops.
It's probably also dripping while driving, and I want to avoid getting my trans and undercarriage coated in oil.

Wondering if the higher pressure could be causing (or exacerbating) the oil leaking around the pan end seals.
(I Replaced the rear main seal recently, and that doesn't appear to be the cause. And recently swapped out to a cast aluminum pan in an effort to eliminate any stamped pan deforming contributing to leaks).
Is the higher pressure also present on the bottom end sump, below the pump? Or only at the top end where the gauge line connects?
Also - does the level of oil affect the pressure? (meaning, if I'm running at a "Full" stick, will that run higher pressure than at "Add" or somewhere in the middle?)
Also/Also - What about the pick-up height? If this is not gapped perfectly to the bottom of the pan, could that also cause the pressure to run higher?

I know I'm grasping at straws, but this last remaining drip/leak has got me at wits end!
If getting the max pressure lowered can avoid these leaks, then "2 Birds" potentially!
Thanks

 

The polite thing to do is delete your posts and start a brand new one with all your questions.
Then we will know all 100% responses are aimed at AZHODGE, and less confusion.