Rocker shaft oil restrictor.... how small is too small

[64PI]

Whats the smallest someone has safely gone? I'm running edelbrock heads with precision pumps bronze bushed rockers. Precision pump M-57HV oil pump. I have a holley 78 jet in the heads now. Priming the pump to 75psi with the valve covers off will flood the heads. I have .003" main clearance and .0025" on the bbc rods. Engine hot @ idle is about 5psi, 50psi @ cruise and 70-75psi @ WOT. The block is half filled and the car runs warmer than I would like. I'm installing an aluminum radiator, electric fan and water pump. Also installing a oil cooler.. I'm just curious if I can go a little smaller to keep some oil down low without completely starving the rockers.

Fred

[GerryP]

The rockers need very little oil.  Your problem with overly restricting oil to the heads is failure to cool the valve springs.  They are cooled only by oil.

[blykins]

I run a .070" orifice for bushed rockers. 

With that being said, it's not a big problem if you get a lot of oil up there.  That's what the drains are for. 

Block filling isn't an issue.  It's not the coolant temperature that will rise, it's the oil temperature.

[blykins]

BTW, the cruise and WOT oil pressures are perfectly fine and normal.  It's the idle pressure that's whopper-jawed. 

What viscosity oil are you running? 

[Thumperbird]

For reference, I've got pretty much the same hardware setup with maybe a little less bearing clearance and run 20 at idle even when engine is up at 200 degrees.  5 does seem awful low and not related to the head restriction.  10w30

[GerryP]

I am going to offer a contrary opinion on your idle oil pressure.  I don't expect very many to agree with me and I'm okay with that.  I am comfortable with my opinion on this one.

Your idle oil pressure is fine.  In that regard, it doesn't matter what weight oil you're using or what your idle speed is.  Idle speed can often make a significant difference in idle oil pressure.  You mid and upper rpm oil pressure is also fine.

The reason I think your idle pressure is okay?  Well, you generally don't see a specification for idle oil pressure.  Not by manufacturers or anyone else.  Oil pressure references are usually specified as oil pressure @ 2,000 rpm or there abouts.  One of the reasons you don't usually see a spec for idle oil pressure is that the engine is under very low load.  It's making just enough power to keep itself turning over.  Because of the very low cylinder pressure, there's very little load on the bearings.  As long as the engine is moving oil over the bearings, you're fine.

The other reason is all engines are subject to stacking tolerances.  These things are not being built to aerospace specifications so bearing clearances may not be completely uniform throughout the engine...particularly in the camshaft where most oil pressure is lost.  It's good enough to get the job done.

Some old timers may recall this, but it was pretty common for the oil light to flicker when you were sitting at a stop light at idle.  The pressure sensor would turn on the light around 5psi.  This was with brand new cars.  Ford's solution to customer concerns about low oil pressure?  They raised the idle by 50 rpm and that turned out the light.

If you were concerned about idle oil pressure you could try running a slightly higher idle or, depending upon what you're now using, running a heavier oil.  But I don't think you need to.

[blykins]

I am going to offer a contrary opinion on your idle oil pressure.  I don't expect very many to agree with me and I'm okay with that.  I am comfortable with my opinion on this one.

Your idle oil pressure is fine.  In that regard, it doesn't matter what weight oil you're using or what your idle speed is.  Idle speed can often make a significant difference in idle oil pressure.  You mid and upper rpm oil pressure is also fine.

The reason I think your idle pressure is okay?  Well, you generally don't see a specification for idle oil pressure.  Not by manufacturers or anyone else.  Oil pressure references are usually specified as oil pressure @ 2,000 rpm or there abouts.  One of the reasons you don't usually see a spec for idle oil pressure is that the engine is under very low load.  It's making just enough power to keep itself turning over.  Because of the very low cylinder pressure, there's very little load on the bearings.  As long as the engine is moving oil over the bearings, you're fine.

The other reason is all engines are subject to stacking tolerances.  These things are not being built to aerospace specifications so bearing clearances may not be completely uniform throughout the engine...particularly in the camshaft where most oil pressure is lost.  It's good enough to get the job done.

Some old timers may recall this, but it was pretty common for the oil light to flicker when you were sitting at a stop light at idle.  The pressure sensor would turn on the light around 5psi.  This was with brand new cars.  Ford's solution to customer concerns about low oil pressure?  They raised the idle by 50 rpm and that turned out the light.

If you were concerned about idle oil pressure you could try running a slightly higher idle or, depending upon what you're now using, running a heavier oil.  But I don't think you need to.

I look at it this way.....

I build a ton of FE's, with the same bearing clearances and the same oil pump, and I have never witnessed anything lower than 20-25 psi on a hot idle.  Even with a standard volume/standard pressure pump, I still see that much idle pressure. 

Based on just a very large sample size, I can say that something "ain't right". 

Now, it could be a gauge that's off, or it could be the combination of a lighter viscosity oil with a poured block and no oil cooler.   Either way, 5 psi at hot idle isn't normal and I'd be checking it out. 

[GerryP]

Okay, I'm not surprised you don't see it as normal.  But is it harmful?  You write what normal idle oil pressure is.  What establishes a norm?  What happens if it's 40psi or 50psi at idle?  I've seen that plenty of times.  I mean, the  often stated rule is that you need 10psi/1000rpm and that gets thrown around as though it were gospel.  Is that always the target pressure?  If you had a customer engine with great oil pressure all the way around but with 5psi at hot idle, what would be your remedy?

[blykins]

Okay, I'm not surprised you don't see it as normal.  But is it harmful?  You write what normal idle oil pressure is.  What establishes a norm?  What happens if it's 40psi or 50psi at idle?  I've seen that plenty of times.  I mean, the  often stated rule is that you need 10psi/1000rpm and that gets thrown around as though it were gospel.  Is that always the target pressure?  If you had a customer engine with great oil pressure all the way around but with 5psi at hot idle, what would be your remedy?

If the gauge and oil were known to be correct, I'd probably be tearing it down to see what's wrong.   

[mikeelikee]

what does the oil pressure do at idle, 2500 rpm, and 4500 rpm? Not suggesting this is the issue but it has happened to a few folks.

[64PI]

Brad Penn 10W30 oil.. 3/4 groove main bearings.  Idles at 900rpm in park. At 1200rpm it starts to climb... 1500 rpm 25-30 psi.
The oil pressure is very responsive to RPM and does not fluctuate at cruise or wide open or even holding steady at 1500. No debris in the oil filter.. All the galley plugs are in it. EDM lifters. No noises, clings, clangs or bangs. Engine runs very strong.. Just runs on the warmer side of life which I am addressing. I thought I could get away WITHOUT an oil cooler and I don't think that is possible with a half filled block. Plus my 2 1/8" cross over headers are not helping any. 

[blykins]

Brad Penn 10W30 oil.. 3/4 groove main bearings.  Idles at 900rpm in park. At 1200rpm it starts to climb... 1500 rpm 25-30 psi.
The oil pressure is very responsive to RPM and does not fluctuate at cruise or wide open or even holding steady at 1500. No debris in the oil filter.. All the galley plugs are in it. EDM lifters. No noises, clings, clangs or bangs. Engine runs very strong.. Just runs on the warmer side of life which I am addressing. I thought I could get away WITHOUT an oil cooler and I don't think that is possible with a half filled block. Plus my 2 1/8" cross over headers are not helping any.

Most filled blocks need oil coolers, hard to get away from it.   Makes oil temp go up. 

I think I'd try some 20W50 BP oil to help with the higher temperatures and if that didn't work, I'd be looking to see what's up.   Old worn out pickup 390's will make the oil pressure light come on.  New engines should not.

It might be worth it to try another oil pressure gauge first.

[64PI]

Brent-  have you ever checked oil temp before on a filled block? Just curious what kind of difference I will see in temperature by adding the cooler. And the better question is what kind of affect does that temperature difference have on viscosity? I picked up a pretty decent size cooler. I believe it’s 32 row 11”x8”x2”.

[blykins]

I take oil temp readings on all the engines I dyno.  I see 10-15 degrees difference usually. 

Got another gauge to try real quick?

[GerryP]

My oil cooler is a little smaller.  An Earl's 16 row plate cooler.  I've never measured the temps but it's a pretty big drop.  At idle, the oil hose going in is too hot to touch for more than a couple seconds.  Oil coming out of the cooler is a lot cooler.  Cool enough you can hold the hose.