oil pressure spec?

Dave-R · Post by **Dave-R** » Sun Sep 02, 07 2:47 pm

What was that rule of thumb about what psi oil pressure you should aim for at idle and per 1000rpm?

I used to know this I am sure but can't remember for the life of me.

Dave-R · Post by **Dave-R** » Sun Sep 02, 07 2:55 pm

I just remembered!

Thanks anyway.

mopar_mark · Post by **mopar_mark** » Sun Sep 02, 07 3:46 pm

Dave wrote:I just remembered!

Thanks anyway.

You gonna share what you remembered

Dave-R · Post by **Dave-R** » Sun Sep 02, 07 6:08 pm

Nothing less than 15-20psi even at idle. Otherwise you risk engine damage.

50psi at 5000rpm and 10psi per 1000rpm above that.

These are minimum values.

Dave999 · Post by **Dave999** » Wed Sep 05, 07 4:56 pm

unless you run a hemi 6 in which case you have no chance of maintaining 15PSI at idle once its hot 10 most likely

and you will rip the cog off the drive or snap the pump snout if you shim the pump relief spring to give you any more than 60 at any RPM

so thats me a Matt sorted as well

Dave

Dave-R · Post by **Dave-R** » Wed Sep 05, 07 7:09 pm

Yet the slant six uses the same pump and pressure spec as the B and RB engines.

Pete · Post by **Pete** » Wed Sep 05, 07 8:22 pm

I thought Chrysler stated 10 psi at idle was OK, and yes we would all like more than that. I think the simple oil lights come on at about 5 psi

Dave-R · Post by **Dave-R** » Wed Sep 05, 07 10:25 pm

Pete wrote:I thought Chrysler stated 10 psi at idle was OK, and yes we would all like more than that. I think the simple oil lights come on at about 5 psi

MP reccommend that you fit an ignition cut out device that kills the engine when oil pressure gets down to 15psi on performance engines. So they must be worried about pressures of 15psi and lower.

Anonymous · Post by **Anonymous** » Thu Sep 06, 07 10:40 am

My understanding is that it only takes 5psi to actually float a bearing, especially if engine speeds are low (as at idle).

The bearing pressure is related to surface area and grooviness of bearings, plus a few other factors regarding positive or negative displacement pumps, lifter efficiency and fitting of the lifters in their bores.

The other factor is the design of the engines and the oiling system. Not too au fait with MoPars but other engines I have dealings with, Buick V6 and V8's and Ford FE's and Clevelands are, supposedly, weak in their oiling systems.

The position of the oil gauge sender is important. Many cars have the sender very close to the pump and hence get a true pump reading which is not necessarily what parts of the rest of the engine are getting. Some Buick V8's (again, dependant on quality of build) can bleed off almost 20psi of oil pressure across the bearings front to back. Hence if you are idling at 20psi at the gauge, you can have 5psi or less at the rear mains. Ford Clevelands can do this as well, leaving the rear mains and rods a bit 'short' of oil. This tends to be afunction of, strangely, oiling the cam bearings first, and then feeding the mains off the cams. The Americans make quite a fuss about this on Clevelands but Australians are much more relaxed, preferring to worry more about sump baffling to keep oil at the pick up as they hoon around bends rather than worry about oil surge when they launch.

I suspect that it is the worry about pressure bleed off rather than the intrinsic worry of bearing float pressure that insists folk keep idle oil pressure above 15-20psi.

My GN used to idle at about 15 psi at 600 rpm, but the gauge moved instantly you touched the accelerator and was reading 30-40psi by the time you hit 1000-1200rpm.

Not sure if that contributes anything, but my thoughts anyway.

Too high oil pressure at cold start is very bad as well.

All the best

Blue · Post by **Blue** » Thu Sep 06, 07 11:40 am

I too would be worried about less than 20 psi at idle, although that's based more on gut feeling that hard facts. V8 Mopars take the pressure reading at the opposite end of the engine from the pump and off the end of the lifter gallery if I remember correctly. In that position I think it pretty much gives you worst case scenario pressure wise as it's reading after the bearing and lifter "leaks". I actually have too much oil pressure on the 440, I noticed it creeping above 100psi at the top end of the track. I'll be dropping out the 20/50 and filling it with 10/40 before the HRD's to see if that does the trick, failing that I'll ll fit one of those Milodon adjustable bypass valves and dial it in that way.

MilesnMiles · Post by **MilesnMiles** » Thu Sep 06, 07 1:27 pm

how much is too much at cold? Since moving to thicker oil I get 80psi at cold. I never Bananarama! until it settles down to its customary 65-70psi (x 3000rpm) when hot.

Dave-R · Post by **Dave-R** » Thu Sep 06, 07 3:36 pm

Never never never thrash an engine until it is at or only just below full temp.

Dave-R · Post by **Dave-R** » Thu Sep 06, 07 3:37 pm

In fact. I don't even move mine off the drive until the gauge starts creeping up.

Dave999 · Post by **Dave999** » Thu Sep 06, 07 3:49 pm

slant six is a different beast to a hemi 6

slant six only has 4 mains a hemi 6 has 7

hemi 6 oiling is marginal at all RPMs but they last ok

not surprising when the manual states if the standard bearing is causing stiffness in rotating the crank when assembled replace the engine case half with the next thinner size??????

anyway the pump flows enough its just rubbish on the pressure front

gear is press fit like most
go over about 60 psi and the gear comes off
weld the gear on and you distort it or alter the properties of the shaft
gear runs on cam that has no thrust face so the cam wanders and snaps the pump snout off.

aftermarket cams are made from chevy blank billets their dissy and oil pump gearing never matches the standard hemi pump. and the billets are too thin mainly to allow for higher lift and smaller base circle so you can fit them into the cam tunnel. major harmonic issues with a cam that thin and that long which of course ruins your oil pump and dissy

presure relief spring is made of string as well but 2 1/2 pence pieces under it should see you hit 45 PSI at about 5000 rpm when its sunny and hot.

flywheel is only held on with three bolts as well

and so is the clutch

both fall off and ruin You or your crank with alarming regularity

Dave