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Oil Pressure
liam.mccaffrey - 9/12/08 at 11:52 AM

I have a couple questions on oil pumps for anyone running a pressure gauge.

I know this isn't engine specific but a ball park is fine.

1. What is you idle oil pressure?

2. What is your max oil pressure?

3. Does anyone know what kind flow rate they are getting from their pump?

If you have any info on this I would be very grateful.

Liam Mc

[Edited on 9/12/08 by liam.mccaffrey]

BenB - 9/12/08 at 11:56 AM

You going dry sump?!?!?!

Mr Whippy - 9/12/08 at 11:59 AM

varies massively between engines

my pinto idles at about 60psi

v6 about 20psi!

scared the crap out me till I asked an engine shop guy who showed me a big book with all the rating in it and turned out my v6 was just normal

so don't panic if you have a low reading, just find out what the normal values are for that engine



[Edited on 9/12/08 by Mr Whippy]

BenB - 9/12/08 at 12:38 PM

Flow rate will depend very much on pressure.... Each pump will have a different flow:pressure curve.....

liam.mccaffrey - 9/12/08 at 12:39 PM

I know that each pump has a specific flow pressure curve, but how quickly would you expect an engine to cycle its full oil capacity.



[Edited on 9/12/08 by liam.mccaffrey]

02GF74 - 9/12/08 at 02:00 PM

quote:
Originally posted by BenB
Flow rate will depend very much on pressure.... Each pump will have a different flow:pressure curve.....


hmmm. not sure I would agree with that.

try this for a demonstration.

1. take a 1.0 litre Tesco bottle of fizzy water, shake the bottle, place it horizontally and then make a tiny hole in the cap. You should see a jet of water come streaming out quite a long way.

2. as above but remove the cap. you will get more water come out but it wil not travel as far.


example 1. is high pressure, low volume and example 2. is low pressure high volume.

so back to oil pumps.

pressure exists if there is a resistance to flow; in an engine it would be the small gaps between mains bearings etc. To prevent the pressure getting to high , there is a relief valve - usually as spring loaded plunger that opens a bypass.

The amount of flow is determined by the size (i.e. volume) and speed the rotor turns.

and returning to the original question.

oil pressure varies for different engines, e.g. rover V8 limited to 30 psi, MGB B series 80 psi.

I have never worked out oil flow so cannot answer that part of the Q.

coozer - 9/12/08 at 02:15 PM

My zetec starts up from cold around 70psi, idles at 40 once warm and goes up to 80 when giving it the beans.

My gauge reads the pressure in the cylinder head tho and not the block.

Steve

Mr Whippy - 9/12/08 at 02:54 PM

quote:
Originally posted by coozer

My gauge reads the pressure in the cylinder head tho and not the block.

Steve


should be the same pressure in both the block and the head as the supply oil ways are quite large between them and not enough restrictions to produce a notable pressure drop. In areas where there is oil pouring on to a part, like the pintos cam there is a restrictive drilling before the opening to maintain the oil pressure behind it.

[Edited on 9/12/08 by Mr Whippy]

flak monkey - 9/12/08 at 03:01 PM

Pinto is about 40-50 psi ticking over and 100-110psi when driving. Thats with a high pressure and high capacity pump. Not sure what it would have been with a std one.

Cheers,
David

Mr Whippy - 9/12/08 at 03:37 PM

quote:
Originally posted by flak monkey
Pinto is about 40-50 psi ticking over and 100-110psi when driving. Thats with a high pressure and high capacity pump. Not sure what it would have been with a std one.

Cheers,
David


wow mines got a high pressure pump too but only gets to 80psi!

liam.mccaffrey - 9/12/08 at 10:29 PM

interesting

http://www.aa1car.com/library/2005/us020516.htm

02GF74 - 10/12/08 at 10:19 AM

^^^ good article .... is what I said in about 1/50 of the words!

good point about smoothing out the edges in the oil pump - I have done this to crossflow pup as well as mocal take off plate, the performance increase is phenomenal!!

(ok, I had some spare time and went crazy with the dremel!)

liam.mccaffrey - 10/12/08 at 10:41 AM

I did a big long reply to your post last night and then lost the lot (along with the will to live)

Check the DVApower site about 2 thirds down. FLowing oil pumps

http://www.dvapower.com/


[Edited on 10/12/08 by liam.mccaffrey]

MikeRJ - 10/12/08 at 12:50 PM

quote:
Originally posted by flak monkey
Pinto is about 40-50 psi ticking over and 100-110psi when driving. Thats with a high pressure and high capacity pump. Not sure what it would have been with a std one.

Cheers,
David


You might want to reduce that a fair bit. Very high oil pressure doesn't provide any more protection, but does absorb more engine power and make the oil hotter.

02GF74 - 10/12/08 at 01:49 PM

what ^^^ he said; mnot to mention more wear on the oil pump drive.

liam.mccaffrey - 10/12/08 at 02:56 PM

this will be a very interesting project,

Await my masterpiece people

Thanks for all you help

britishtrident - 10/12/08 at 03:55 PM

Back in the days when cars had engines you could tinker with it was not uncommon to find cars with a few miles on the clock only producing about 7 psi at idle speed when hot --- this was OK provided the engine started to buil up a reasonable oil pressure at over 1200 rpm.

So what is a reasonable pressure ? To lubricate the bearings you don't actually need much pressure, the job of the oil pump is simply to deliver a supply of oil to the bearing. The hydrodynamic action within bearing actually generates a much higher internal oil pressure which is what what keeps the wearing surfaces of the bearing surfaces apart.

Normal working oil pressure depends on a three main factors.
(1) Bearing clearance and condition.
(2) Oil viscosity
(3) Oil pump (size & condition)

In addition the oil pressure at cold start should be controlled by pump the relief valve.

High oil pressure is not an end in it's self, in fact as already mentioned it wastes power and can cause damage to an engine --- On the old Rootes 1725 engines I have seen top quality Fram PH9 oil filters blown clean off their bases by stuck relief valves.

About 80 psi should be regarded as the maximum you should ever see on an engine hot or cold any more than that you risk the filter failing at the rolled seam around the base.

At the low end 20 psi when hot is actually more than enough to lubricate and cool the the bearings but if an engine that normally produces 50 psi at say 2000 rpm drops to 30 psi start to worry.

[Edited on 10/12/08 by britishtrident]