Motor not building oil pressure

[dawdaw]

So just got done putting my neighbors 455 olds motor together the other day... The motor was broke in properly and has perfect compression across the board... the whole motor was spec'd out by lsm engineering... The motor is comprised of the factory crank, H beams, Diamond pistons, Factory ported C casting heads with a .609 valve lift roller cam with the duration in the 250's at .050... We've drove the car a few times now and it doesn't smoke at all and seems very healthy (car ran bottom 11's in a 4200lb car and driver), We simply refreshened the motor because the stinking thing had over 700 passes on it! Odd thing is we started the car up with 10w40 oil, and being fully warm it was holding 35lbs of oil pressure at 1000rpm idle, and had 65 to 75 on WOT... now that the thing has been broken in it only hold 20 at idle, which isn't the issue, but when it hits 2000 rpm the oil pressure does not build past 40lbs even at the 6000 rpm limiter.. The car has oil on the plugs, so went through and checked the valve seals and guides and that is not the issue and we know it's not coming threw the rings becuase of the compression being 200psi on every cylinder (give or take 2 or 3 psi variance) with 9.0:1 static motor with a cast iron head... So basically we are trying to find out why the thing does not build more then 40 lbs of oil pressure past 2000 rpm.. please any advice would be appreciated becuase we are scratching our heads on this thing..

Car has a high volume/standard pressure oil pump with 20w50 brad penn it... We put 2 different mechanical gauges in it to make sure it wasn't the gauge..

[firebird_1995]

Is that the same oil pump it was running before?

[dawdaw]

Is that the same oil pump it was running before?

Yes, everything stayed the same as the previous motor...

[firebird_1995]

The only thing it could be is bearing clearances. What's the chances it originally had turned rods or mains and standard bearings got put back in?

[popo8]

FIrst, have you tried a different sending unit and guage?

[joelster]

What oil filter do you run? Go get a NAPA Gold on there. My car picked up 5-10lbs switching from a pos Purolator filter. The filter could be a small bottleneck even if the bypass is wide open.

[MeanTA]

i would say check the sending unit.

[firebird_1995]

We put 2 different mechanical gauges in it to make sure it wasn't the gauge..

Its not the sending unit

[firebird_1995]

Hey I just thought of this... I had a 400 Pontiac once and it had low oil pressure. When I tore into it I found it had an freeze plug type plug in the oil galley that had came out in the timing chain cover. Does the 455 olds have these type plugs? They are in the timing chain cover behind the cam gear

[dawdaw]

The only thing it could be is bearing clearances. What's the chances it originally had turned rods or mains and standard bearings got put back in?


Bearing clearances were like from .0028 to .0030 and on the thrust bearing like .0033... I highly doubt it's bearing clearances


FIrst, have you tried a different sending unit and guage?

yup 2 different mechanical ones


What oil filter do you run? Go get a NAPA Gold on there. My car picked up 5-10lbs switching from a pos Purolator filter. The filter could be a small bottleneck even if the bypass is wide open.

It's a pro systems oil filter.... It's like a stainless filter element for a fuel system, they're pretty neat... You just pull it off and brake kleen the snot out of it.. We have tried 3 different filters on it, and getting same results


i would say check the sending unit.

We checked it with 2 gauges


Its not the sending unit

yup lol


Hey I just thought of this... I had a 400 Pontiac once and it had low oil pressure. When I tore into it I found it had an freeze plug type plug in the oil galley that had came out in the timing chain cover. Does the 455 olds have these type plugs? They are in the timing chain cover behind the cam gear

yes they do... They have small "squirters about .040 big that shoot oil onto the timing chain in the front of the motor, and one for the rear that shoots oil onto the cam gear for the dizzy..

[Madman337]

Check the oil pressure relief spring, not the one in the filter in the pump
I have seen these things fail and it can cause low oil pressure and bad cam bearings can cause low o.p. as well.