Oil Pressure after Rebuild

[Alan Winer]

I did search the forum but was unable to find anything specific. What oil pressure should one expect at idle and at speed after a complete rebuild? Should I expect higher than normal readings? Engine is a 616/15 356C with 86mm bore kit installed.
Thanks,
Alan

[C J Murray]

30-70psi hot, idle to 4000rpm.

[David Jones]

Initial max oil pressure will depend entirely on the oil pressure relief valve spring tension and eventual hot oil pressure will depend on rpm, bearing clearance and viscosity of oil. Hot idle pressure should be at minimum of 7 psi to keep the oil pressure light out. I would say 40 psi hot at rpm and no less than 7 psi hot for idle but that is just my experience with stock parts. I would guess that race engine will run higher hot pressures. I used to run a 60 psi spring on the race car but once at race temps usually never saw that pressure unless at max rpm.

[Ron LaDow]

The Spec Book states "'warm engine, idling' - 0.5Atm (~7PSI) min, warm engine at 2.5KRPM - 3.0Atm (~45PSI), 2.0, min."

[Craig Richter]

C J, Sometimes your use of English language does baffle me. Did you mean 30psi hot idle, 70psi hot 4000rpm, or what? Stock stuff won't normally put out those numbers.

[Ron LaDow]

C J, Sometimes your use of English language does baffle me. Did you mean 30psi hot idle, 70psi hot 4000rpm, or what? Stock stuff won't normally put out those numbers.

(once again, we experience the frisson regarding the size of the image and the steam-powered Registry software!)

IT WORKED!
Craig, that part you see was the prototype of the Pre Mat Full Flow, and the brass plug is blocking off the port where we sampled the pump output prior to passing through the filter (barely visible above and to the right is a plug blocking off the port where tested the pressure to check the drop across the filter element). At the brass fitting, we saw well over 250PSI at well under 5KRPM.
I'd spent some time 'blue-printing' the pump, which I'll never do again. That 'large' pump is not far off the size of a SB Chev pump with something like 4-5X the bearing 'leakage' area of the 616 engine (that which determines how much the pump needs to deliver).
Measuring the pressure at the stock location, we found pressure quite a bit higher than the Spec Book claims; I'm saying that pump, in a fresh engine overpowers the relief valve.
Now, if you have an engine with the stock 'filter', it certainly won't take long for the bearings to 'wear in' and your pressure to drop.

[Neil Bardsley]

My Pellow engine is generating about 40/60 at start up.

For a race engine is there any advantage to running lower oil pressures in the engine? I once read a registry interview with Michael May there he talked about reducing the pressure on the 4 cam engine which generated more power?

[Alan Winer]

I understand their are many variables affecting oil pressure, but I was trying to determine whether a newly rebuilt engine would have higher oil pressure levels until some point of break in.
Alan

[Martin Benade]

Ron, you don't think the relief valve was stuck? Are the passages in it that small not to bleed off the pressure when it is working?

[C J Murray]

C J, Sometimes your use of English language does baffle me. Did you mean 30psi hot idle, 70psi hot 4000rpm, or what? Stock stuff won't normally put out those numbers.

If I write in German you will be more confused!

Now, if you have an engine with the stock 'filter', it certainly won't take long for the bearings to 'wear in' and your pressure to drop.

Shameless self promotion! I like it.

For a race engine is there any advantage to running lower oil pressures in the engine? I once read a registry interview with Michael May there he talked about reducing the pressure on the 4 cam engine which generated more power?

I bet the F1 guys have that down to a science and the factory would have had the resources to blow up engines during extensive testing but us mere mortals err on the safe side. Air cooled engines are really air/oil cooled and playing around with oil circulation is very dangerous. Modern engines in the electronic age sometimes utilize electric pumps for moving fluids but what does that do to the effort required to generate electricity? Of course charging the battery could be delayed and done while the engine isn't using peak power.

There are many variables to the answer to Alan's question. Relief spring pressure, bearing clearances, idle rpm, location of sensor, and oil viscosity to name a few.

The Porsche spec numbers are for a worn out engine.

You get much lower pressure at 700rpm than at 1000rpm. I don't like a real low idle because it is hard on the camshaft.

My gauges have been reading from the factory position near the distributor.

Cold starts at above idle rpm approach 100psi quickly.

I use Mobil 1 V-Twin 20w-50.

Hot idle 1000rpm somewhere near 30psi. Hot high rpm over 70psi.

I like the old rule of thumb, 10psi per 1000rpm, but life is never that simple so don't be trapped by absolute numbers.

[Neil Bardsley]

Just to be clear and not to side track too much

"You get much lower pressure at 700rpm than at 1000rpm. I don't like a real low idle because it is hard on the camshaft."

Your preferred idle speed is 1000rpm? This gives you more oil pressure or you also like a higher idle for another reason?

I've often heard people talking about zinc in the oil for the tappets on the cam however I don't think I've ever heard of another complaining of an engine failure from broken cam? I admit they are at the bottom of the engine so not easy to replace but normally it's piston, rod or crank and these aren't helped by zinc in the oil but by using a higher quality synthetic oil?

[Vic Skirmants]

Cam failure alluded to by Cliff is WEAR, not breakage.

[C J Murray]

ZDDP in oil contains zinc.

Yes, a low idle doesn't splash as much oil and less oil is being flung around from the connecting rod bearings onto the cam.

[Neil Bardsley]

I don't think the oil has lead.
Cam failure alluded to by Cliff is WEAR, not breakage.

Sorry Vic changed to zinc. I was just asking if high level of zinc is really needed. As many on here prefer/suggest mineral oils with higher levels of zinc to modern synthetic oils.

[Ron LaDow]

Ron, you don't think the relief valve was stuck? Are the passages in it that small not to bleed off the pressure when it is working?

The only 'problem' with the relief valve was the inability to dump enough pump output volume to keep the pressure down to spec with a blueprinted pump and bearing journals; the pump output exceeded the relief valve passages under those specific conditions.
My theory has to do with (1) warrantee rebuilds, and (2) that pathetic excuse for filtration hanging on the fan housing, and the cheapest engineering solution to solving (1) without spending tons of money correcting (2): Stick a pump in there big enough that the volume kept pressure even at .5mm clearances.