I recently aquired a 426 mopar crate hemi that apparantly ran really well/strong,but has lowish oil pressure when hot.it came to me minus oil pump so I am going to order a pump for it today.Should i get stock replacement or hi psi or hi volume pump for it? i plan to run it as is for now...

what psi? (idle & at speed). confirmed with a good mechanical gauge?

I would go through it BEFORE installing it!

"High pressure": strong relief spring
"High volume": taller gears
Other problems:
too much oil diverted to valve gear
loose bearings

What weight oil was used in it and how much pressure is "low" ?
I like and use the old rule of 10 lbs. per 1000 RPM with hot oil, in other words 20 lbs. at 1000 RPM is good as long as it has 65 Lbs. at 6500 RPM
I like and use 5W20Wt oil in all my street toys now
My old 518 C.I. pump gas wedge stroker motor had 70 lbs. cold at 1200 RPM with 5W20Wt. oil, it had 18 to 20 Lbs. idling at 800 RPM with the oil temps north of 170 F and it had 65 Lbs. max above 3000 RPM with hot oil.
I had to trim the high volume bypass spring 1 1/2 coil to get if down that low after running the motor, stock it would have 80 lbs. cold idling and make the bypass spring work above 3000 RPM (it would bypass at 80 Lbs> no matter what the oil temps. where

Mopar crate Hemi = Take it apart and look.

The crate Hemi engines that I've seen appeared to have been built by small children at Mary's school for the blind. If a crate Hemi came into my shop with low oil pressure I'd tear it down. Last thing I'd do is put a new oil pump on it. I bet the bearings are shot.

Oil pump missing? Not a lot of reasons for that except to hide evidence of the rod bearings being pumped thru it but I'm getting cynical in my old age.

For the price of a pan gasket it's cheap insurance to know it still has useable crank bearings in it while all the rods are still inside it.
If it's an MP crate, not all of them get glowing reviews in the quality control department.

Kevin

I'd inspect the entire engine as well. Given the stupid costs of all things hemi, bearings, rings and honing and possibly turning the crank are peanuts.

My engine is about 5 years since the build, and has about 12 lbs at idle, after being on the highway for a bit. The engine runs cool, 170-190, but after pulling off the highway, will drop down that low. All it needs is a few hundred rpm to be back in the 20+ range, and pressure climbs with RPM to 60-70+ lbs.

After a little city driving, the idle pressure climbs back up to around 20 or so, so it does seem to be an oil temp issue.

I run 20-50, but next time am going to try a straight weight. The bearings are all .005 or so on the loose side. I'd have to look up exactly what they are. I got all the internal components from Tim at FHO, and he said put it together, that's the clearances he wanted to see.

Anyway, it is a little disconcerting. I don't let it sit long at that pressure, if I'm at a light or something I'll rev it every 10-15-20 seconds or so to get the pressure up a bit.

if there's doubt or questions take it apart. as for pumps I've got a combo I like very well. high volume pump with a stock pressure relief spring. I don't run loose clearances either.

As stated, I would go thru it first and check clearances. Hemi's like putting oil up top in the heads, so if you don't have a big 12quart pan and put a big pump on it, oil pressure will not only get worse, it may lock right up.

Straight weight 50 vs 20w50 will do nothing. Its 20w vs 50w cold, not hot. What you have is enough flow paths hot to reduce pressure when the oil is thinner due to temp. So is the oil temp too high? Or is there to much internal leakage? First off I'd be measuring oil temp. Water temp seldom correlates to oil temp. Is the oil temp in range? Then you have a decision. Either your build has excessive leakage in the lifter bores, valve train, drain back issue, etc. Or the engine is in trouble. If you're confident there is no issue, the high volume pump will help. Make sure there is sufficient capacity in the pan.
Doug

Makes sense, thanks.

thanks for the input guys,i know almost nothing about the engine,came from a friend of a friend who said it ran really strong except for that one issue.I likely will pull the pan off and have a quick look before i run it but doubt I will do a full teardown.I have no idea the actual psi #s unfortunately....

IMO, get a high volume pump and then manipulate the pressure to your liking w/ the spring. Either trim the spring or shim the cap out w/ an extra gasket or two to drop the pressure.

Dragula...like I've said before, you don't need a 12 quart pan to keep a hemi out of oil starvation. You need to control where the oil you have is going. Your last combo had an issue somewhere that was putting oil somewhere it shouldn't have and starved the vitals. Your big pump and 12 quart pan was a bandaid at best and even that didn't work did it? My 572" hemi has 7.5 quarts in it and survives just fine turning 7500 rpm. Same setup since 2006.

I understand you not wanting to do a full teardown. Some people don't want to open that can of worms. The regular Mopar/Melling high volume pump should get you where you want to be. In the old days when I would buy a tired street hemi (these things were always tired) if it didn't have enough oil pressure I would put 50w Valvoline racing oil in it. And if that didn't bring it up I would put a hi volume pump on it. That always solved the problem. These were tired motors with 50,000 miles or 10 years on them. No telling what the clearances were. Good luck.

If it was mine I would look at all the rod bearings, tops and bottoms, and replace any I didn't like, same thing on the mains

Never had a 12 quart pan....gonna have one this time around. Was told by multiple engine builders, my junk was all set to go...We usually see mopars with low idle oil pressure that have excessive crank clearances. We deck the caps and re-line hone. We did this twice on my Hemi...

On putting spacers behind the spring, has anyone ever checked to see how much it would raise the pressure according to how thick the spacer would be? Say, for example 1/16 thick spacer would raise the pressure 10 pounds, or would it do something else?

Adjustable oil pressure!
https://www.jegs.com/i/Milodon/697/21550/10002/-1