I put this in here because i have contacted several people searched a ton and i figure its an advanced problem because i cant fined an answer so here it goes.
Story is i bought the engine used with low miles. I pulled the pan to check the bearings before putting it in. I found the mains and rods had more wear then i would to have liked to see for a engine with less then 10,000 miles. The pickup was bent way up and not aliened properly. So i purchased a new melling select 10445 oil pump and pick up get the pickup set to specs, new clevite main and rod bearings and new arp rod bolts. All torqued to spec using the moly lube ect. Got the pickup welded and put it in the car. The engine runs fine has 70-80psi cold idle. After warming it up it has around 40psi hot and 70psi at the touch of the gas. Now making a wot pull 1-4th oil pressure will go to 70-80psi quickly drop to 40psi around 5000 rpm's then climb back up to 70psi by 5300-5400 and hold to the gear change. It will do this in every gear except fourth where it does not drop at all. So i verified it with a mechanical gauge same thing my stock gauge is dead on. The windage tray is in place and in the right direction and torqued to 25 ft/lb's. That was the first thing that came up in a search. Then i contacted a local engine shop and they said it sounds like the relief in the pump is getting caught up so i ordered a pump through them brought them my pan and had them set the pickup clearance and weld it. While i had it off i pulled a main to check one the bearings (looked new) and two that little ball thats supposed t be in there. I also went ahead and put a new filter adapter in from Gm. I get it all back together and it does the same damn thing. Any ideas? Everyone i talk to is astonished. Another thing to add is it does leak a couple drops of oil thats by the rear of the motor when i park it over night but im pretty sure its coming from the intake gasket. Any help at all. I had some pretty big plans for this engine but with a oil pressure issue im not about to dump money into if its going to take out my high dollar parts (ex heads cam)

Any ideas?

lt1 Engine has
Stock crank chamfered
Eagle forged I beam rods
Trw forged pistons
Clevite H series rod and mains stock sized
Bearing clearances are 3-4 thousandths

 

How did the cam bearings look when you inspected them?

 

Didn't get a chance to check those, really didn't want to pull the timing cover off until i did a cam swap, because i hate the cam he put in it.

 

Alright. Then let's try something a little less involved than a complete teardown.

Have you tried adding a little extra oil to see if it is a starvation issue at the pickup? (ie, overfill the crankcase slightly)

Low pressure with a known good pump is caused by one of two things:

1. Not enough volume on the intake side of the pump (clogged pickup or oil moving away from the pickup or pickup simply not located correctly)
2. Not enough restriction on the output side of the pump (relief valve opening up, as thought previously, or an intermittant failure of another component resulting in too much oil returning to the pan)

The windage tray look ok and is present? Is it installed properly? (not trying to sound like an *** or make you sound stupid.....but, we have to cover all bases in our troubleshooting)

 

u cut up the oil filter yet?

 

I appreciate all the help. Any questions help. The windage tray is in and installed properly and torqued to specs. I haven't tried adding more oil yet. I have cut the oil filter open did not see anything out of the ordinary. I have tried using the ac delco filter as well as the mobile 1. The screen is not clogged. I check the old one when i pulled it out and the new one definitely is not. The pickup was set by me the first time around and the second time around I gave them my pan and paid them to do it on a new oil pump. I am trying to follow your though process and think of what could let the oil drain back to quickly.

 

"Bearing clearances are 3-4 thousandths"... Huh??

 

The front four mains were .003 and the last one was .004. If i remember correctly the rods were .002. plastic gauge was used to measure.

 

You need to check your oil pump drive , i bet the teeth are all eat up on it causing your intermittant problems. You need to pull the intake anyway to fix the leak so while your there pull the pump drive out and check it.

 

I dont think its that as it has such low miles. I have pulled the pan off three times i think i would have noticed teeth in my oil pan. BUT i will check it im not going to rule anything out.

 

just pulled the intake off, and checked the drive. Its got all its teeth on it so thats fine. on to the next.

 

I said this on another forum and it looks like Dan Stewart is seeing the same thing I am. Try adding some more oil. Sounds sorta like a G-force thing and the pickup coming uncovered.

 

how much is safe to add? I guess another thing to add is it does not do it in neutral even if it quickly rev it or slowly rev it.

 

Try a half quart at first, then go from there.

 

Well i went out and tried up to 6 quarts it didnt help at all. Its so weird it does it right at 5,000 rpms it drops to 40psi then at 5500 its back up to 70psi, but it wont drop when im sitting still and free reving it slow or fast even holding it at 5000 rpms.

 

Subscribing to this thread... I have the exact same problem and I just rebuilt the entire engine. Everything like said above was to spec. I also have tried up to 6 quarts of oil, and all it did was feel sluggish, like the crank was partially submerged.

 

Im so undecided on what i want to do with this engine. Idk if i should just do the hc like planed and put my nitrous on it. Or i should take it apart and have a machine shop look at it or just get rid of it. Its stuff like this that makes you start hating a car.

 

This is going to sound silly......but,

put it on a dyno where you can run through the gears under load.

If you can repeat the issue on the dyno, you know there is definately a mechanical issue. If not, then it is more than likely a sloshing issue.

 

Is there a bypass valve on the oil pump?

 

Yes and its not sticking because i swapped out the pump for another one and it did the same thing, it is even a different model pump.