oil pressure drop question

[Belgian1979]

I'm new here and was hoping to find some answers here. The subject is a high performance SBC with a high volume high pressure oil pump (anti-cav). Car has a Canton 15-240T pan which is all baffled and has a windage tray +7qrt capacity, it has a B&M HI TEK oil cooler, remote oil filter and Canton Accusump.

I was running a 10W40 halfsynt oil at first in this new engine. Oil pressures cold were up to the bypass setting of 75 when running, 60 on cold idle. During warm up, I was seeing idle oil pressure around 30-35 psi. The issue was that in this high rpm engine I'm seeing the oil pressure drop at speeds over 5000 rpm. I have tried both lowering oil level and more oil in the pan, but it didn't help anything. I changed from the AC Delco PF2 filter to a Motorsports FL1A filter which didn't help either.

Last thing I did was changing to a Valvoline synth. 5W30 and it seemed to improve the idle oil pressure to my surprise, getting around 40 hot. The high rpm oil pressure dropped only 5 psi where it previously dropped 15-20 psi, and it seemed to stay there. Haven't run her up to her rpm limit though.

I was thinking about cavitation somehow, but I'm not sure. Any ideas ? Is there a solution to this ?

Thanks

Yves

 

[440Magnum]

Originally Posted By: Belgian1979
I'm new here and was hoping to find some answers here. The subject is a high performance SBC with a high volume high pressure oil pump (anti-cav). Car has a Canton 15-240T pan which is all baffled and has a windage tray +7qrt capacity, it has a B&M HI TEK oil cooler, remote oil filter and Canton Accusump.

I was running a 10W40 halfsynt oil at first in this new engine. Oil pressures cold were up to the bypass setting of 75 when running, 60 on cold idle. During warm up, I was seeing idle oil pressure around 30-35 psi. The issue was that in this high rpm engine I'm seeing the oil pressure drop at speeds over 5000 rpm. I have tried both lowering oil level and more oil in the pan, but it didn't help anything. I changed from the AC Delco PF2 filter to a Motorsports FL1A filter which didn't help either.

Last thing I did was changing to a Valvoline synth. 5W30 and it seemed to improve the idle oil pressure to my surprise, getting around 40 hot. The high rpm oil pressure dropped only 5 psi where it previously dropped 15-20 psi, and it seemed to stay there. Haven't run her up to her rpm limit though.

I was thinking about cavitation somehow, but I'm not sure. Any ideas ? Is there a solution to this ?

Thanks

Yves



Cavitation in the pump is a possibility, as is the crank itself becoming a centrifugal oil pump and flinging oil out of the crank journal clearances faster than the mains can feed oil into the crank itself. Another unpleasant possibility is a crack through an oil passage that opens up under the stress of high-RPM/high-load operation.

What all has been done to the block oil feeds? Is it a factory production block, or is it an aftermarket race block? Have the feeds to the main saddles been drilled to remove casting flash and assure that plenty of feed volume is available? All the pressure in the world at the oil pump itself isn't going to keep enough volume flowing out to the needed points if there are restrictions in the path.

 

[edhackett]

A drop in oil pressure under load can also be an indication of excessive bearing clearances.

Ed

 

[daves66nova]

Originally Posted By: Belgian1979
I'm new here
You're also from speedtalk!!!

 

[spasm3]

I don't know what pump you are running, but could you be sucking the pan low at high rpm?

 

[jrustles]

Originally Posted By: Belgian1979

I was running a 10W40 halfsynt oil at first in this new engine. Oil pressures cold were up to the bypass setting of 75 when running, 60 on cold idle. During warm up, I was seeing idle oil pressure around 30-35 psi. The issue was that in this high rpm engine I'm seeing the oil pressure drop at speeds over 5000 rpm. I have tried both lowering oil level and more oil in the pan, but it didn't help anything. I changed from the AC Delco PF2 filter to a Motorsports FL1A filter which didn't help either.

Last thing I did was changing to a Valvoline synth. 5W30 and it seemed to improve the idle oil pressure to my surprise, getting around 40 hot. The high rpm oil pressure dropped only 5 psi where it previously dropped 15-20 psi, and it seemed to stay there. Haven't run her up to her rpm limit though.

I was thinking about cavitation somehow, but I'm not sure. Any ideas ? Is there a solution to this ?

Thanks

Yves


Consider that the oil pump bypass valve is a progressively opening orifice. Draw your own conclusions as to why it's relieving more volume pressure as it pumps more volume that cannot escape via the engine, and why it opens less with a thinner oil. The last thing I want to do is ramble on again about oil pumps.

You may find your concern strikingly similar to MINick's in the Motul 5w50 thread.

 

[440Magnum]

Originally Posted By: edhackett
A drop in oil pressure under load can also be an indication of excessive bearing clearances.

Ed


Yes, which aggravates the 'crank acts as a centrifuge' phenomenon.

Excessive main bearing clearances can cause a (small, usually 1-2 PSI) pressure drop at a constant RPM depending on whether the engine is under load or not. Since the crank is fed from the top of the main bearing saddles, net torque out of the engine means net force downward (away from the saddle) on inline and V-type engines, opening the clearance for more oil loss. I've seen several high-miles engines where the (reliable, mechanical) oil pressure gauge would drop a couple of PSI when you pushed on the throttle, and rise a couple when you let off.

 

[expat]

What actual pressures are you seeing at 5000 rpm and over?

Is this a sudden drop?
Do you suddenly see the pressure rise again as the rpm's fall?

 

[Belgian1979]

do you have a link ?

 

[Belgian1979]

It seems to run up to 60 psi when hot and starts dropping over 5000 to about 40 psi. And to answer to one of the other posters, yes I'm from speedtalk as well. This problem seems frequently encountered so there is more to it, i would say. I intend to go to the bottom of it.

Bypass spring is set at 75 psi which is reached when the oil is cold. I see it coming up at 60 psi when rpm goes down, that is correct.

 

[Belgian1979]

high volume high pressure Melling select pump.

I know the 'sucking the pan dry' argument has been out there a long time. I simply am not able to believe that. The people saying this would usually say a std volume oil pump wouldn't do that. However if all the orifices in the engine remain the same, especially those from at the lifters, why would it be able to suck the pan dry unless the return holes were totally plugged (which is not the case BTW) I run a 7 qrt pan with actually 6 qrts in the pan. I do not even think it's physically possible for the valve covers to hold that much oil without the oil spewing out. Furthermore I added oil and it didn't help, on the countrary.

 

[Belgian1979]

Engine has maybe 500 km on it by now. clearance were pretty much std, .0025 on the mains, .0023 on the rods.

 

[Belgian1979]

The bearing shell's oil holes were matched to the holes in the saddles. Block is a 184 bowtie block, nothing special done to the oil channels in the block. If there would be restrictions, i think I would see the oil pressure rise to the bypass spring setting. Oil pressure gauge is on the inlet to the block. I only see 60 psi when hot.It would suggest that it bleeds off too much pressure. Unless that's a problem with bearing clearances opening up, the only other thing in play at that point are the pressurized oiling roller lifters and the spring oilers (although I doubt the latter since the pushrods don't allow more oil up there than normally)

 

[Belgian1979]

Originally Posted By: jrustles
Consider that the oil pump bypass valve is a progressively opening orifice. Draw your own conclusions as to why it's relieving more volume pressure as it pumps more volume that cannot escape via the engine, and why it opens less with a thinner oil. The last thing I want to do is ramble on again about oil pumps.

You may find your concern strikingly similar to MINick's in the Motul 5w50 thread.


I was thinking about the bypass as well however I would have expected it to reach the bypass setting of 75 before it would do that. I do see that the cold pressures reach this bypass setting. I have also been pondering about trying a heavier weight oil, but that would reduce flow as well.

Maybe you could elaborate on this ?

 

[Belgian1979]

I should add that on this pump, the bypass goes to the inlet side. After reading on the subject of cavitation it would seem this is done in order to put higher pressure on the inlet side of the pump in effect delaying the point of cavitation. Since this is occuring at high rpm with a high volume pump at least I would assume the pump is on bypass most of the time and therefor cavitation shouldn't be a problem. However it has also been suggested it might be windage causing air in the oil, which would in effect do the same. However I have a hard time distinguishing between the 2 problems. I already lowered the volume in the pan some 1/2 qrt but it didn't help. I'm bit weary going to far on this.

 

[Belgian1979]

I have to add that I did a test yesterday that involved putting another 700 ml in the pan and contrary to what happened with the thinner 5W30 (dropping 5 psi but staying there) I was seeing the oil pressure drop as well.

To add : I have been pondering over Jrestless' answer and I think I have found what you are aiming at. The valve is indeed progressive and combined with a lighter weight oil when hot, it will allow more oil to exit through the bypass at a lower end pressure. So actually the 60 psi oil pressure when hot is correct vs the advertised spring bypass pressure of 75 psi.Am I correct in thinking this ?

The test from last evening also pointed out that if I fill the oil so that the level sits above the baffle I get windage which induces air into the oil leading to a drop off in pressure.

Now I only need to find out which amount of oil is correct

 

[JethroBodine]

I would try removing the accusump unit and see what happens.

 

[Belgian1979]

I disconnected it so it cannot discharge anymore but it didn't have any effect.

 

[OVERKILL]

May I ask why you fitted a HV/HP pump to an engine with stock bearing clearances?

My buddy bought an SBF with a Melling HV/HP pump on it and Canton pan/pick-up that had lunched itself in a car he got a good deal on because of this. There were signs of oil starvation/cavitation in tear-down, even though this, like yours, had a 7-quart pan. The car was only ever drag raced, not auto-crossed.

When we put the "new" motor together, it got a stock pump and a stock pan (with the stock pick-up being SIGNIFICANTLY larger than the Canton unit) and we had no issues with that engine. This was based on the advice gleaned from an SBF cam guru who went on quite a rant about people putting HV pumps into SBF's because they liked seeing insane pressure on the gauge and didn't really know what they were doing. So what we ended up putting together was a stock low mileage shortblock assembly with all the aftermarket goodies bolted to it from the donor motor, so clearances were obviously stock as well. As was the case with the donor engine from what the PO told us.

I would take a look back at what GM used in their 302 CAN-AM engine that they used in competition against the BOSS 302. My educated guess here is that you may find that what they've used for a pump/pick-up/pan combination is probably close to ideal for what you've built. That was one of the things we found out about the Windsor, that the BOSS 302 oiling system differed only in pan style and pick-up location from the 302HO, and since our conclusion is that Ford probably knew a heck of a lot more about what their engine required for lubrication at 7,000+RPM than the guys telling everybody to run high volume or HV/HP oil pumps, I've heeded that practice ever since.

 

[440Magnum]

Originally Posted By: Belgian1979
The bearing shell's oil holes were matched to the holes in the saddles. Block is a 184 bowtie block, nothing special done to the oil channels in the block. If there would be restrictions, i think I would see the oil pressure rise to the bypass spring setting. Oil pressure gauge is on the inlet to the block. I only see 60 psi when hot.It would suggest that it bleeds off too much pressure. Unless that's a problem with bearing clearances opening up, the only other thing in play at that point are the pressurized oiling roller lifters and the spring oilers (although I doubt the latter since the pushrods don't allow more oil up there than normally)


OK, I keep forgetting the oil flow on SBCs has the gauge at the inlet. I've lived big block Mopar so long I always think of oil pressure gauges as displaying the downstream pressure, but they don't in many engines.

I would think that this confirms something going on on the oil PICKUP side, not the crank/bearings/lifters/etc.

It could be sucking air in the pan- not necessarily "pumping the pan dry," but does the motor have a windage tray? If not, the oil can get swirled into a vortex around the crank and churned to a froth in the pan, so that might be the problem. Finally, the stock pickup tube and screen could be too small for the HV pump, causing the pump itself to cavitate. This might be the best explanation since the effect should get smaller with thinner oil, which you did observe.