how much oil pressure is to much?

[cadamzak]

on a 350 sbc 6800 RPM circle track engine, how much oil pressure is to much. I gotta check the gauge and make sure its not bad but, I am at 75lbs at idle, and 100+ lbs at 4500rpm

[mag2555]

Way toooo much!!!! 20 psi at hot idle and 75 psi @ 6500 is more than enough!

[DaveMcLain]

I just ran into a similar situation with a 383 Chevy engine that I assembled for a customer. It came in all put together but he had me take it all back apart, check it out, put it back together and test it on the dyno. I saw that the engine had a Melling M55HV pump with I think a purple spring. I KNEW I should have changed it because a stock pump is perfectly adequate in one of these engines with proper bearing clearances. Sure enough on the dyno that thing had 100lbs of hot oil pressure and it would idle with 70 or so which I felt was just too much. With the engine still on the dyno I dropped the pan and put in a stock out of the box Melling M55 pump which now gives about 70lbs hot pressure when rev-ed up which is more than enough. I wonder if this is a common problem?

[Belgian1979]

I just ran into a similar situation with a 383 Chevy engine that I assembled for a customer. It came in all put together but he had me take it all back apart, check it out, put it back together and test it on the dyno. I saw that the engine had a Melling M55HV pump with I think a purple spring. I KNEW I should have changed it because a stock pump is perfectly adequate in one of these engines with proper bearing clearances. Sure enough on the dyno that thing had 100lbs of hot oil pressure and it would idle with 70 or so which I felt was just too much. With the engine still on the dyno I dropped the pan and put in a stock out of the box Melling M55 pump which now gives about 70lbs hot pressure when rev-ed up which is more than enough. I wonder if this is a common problem?

Not common imo, my high volume pump has a high pressure spring in it and it gives 75 psi cold at idle, 65 hot and 40 hot at idle. Bearing clearances are .0023 rods and .0025 mains.

Maybe something is restricted somewhere.

[racear2865]

Most HV oil pumps will not produce any more pressure than a regular pump. They just deliver more volume if the bearings allow it. If the bearings will not flow more volume, then it hits the unload. Bearing clearance will determine the flow volume. Sounds like some one swapped to a high pressure spring, which is the only way it will deliver more pressure. That unload spring is what delivers more pressure. You can make a spring change on the M55, and the pressure will go up, if it can handle the additional volume.. The HV pump only has more volume in reserve. The bearings have to flow more.
reed

[machinedave]

I just ran into a similar situation with a 383 Chevy engine that I assembled for a customer. It came in all put together but he had me take it all back apart, check it out, put it back together and test it on the dyno. I saw that the engine had a Melling M55HV pump with I think a purple spring. I KNEW I should have changed it because a stock pump is perfectly adequate in one of these engines with proper bearing clearances. Sure enough on the dyno that thing had 100lbs of hot oil pressure and it would idle with 70 or so which I felt was just too much. With the engine still on the dyno I dropped the pan and put in a stock out of the box Melling M55 pump which now gives about 70lbs hot pressure when rev-ed up which is more than enough. I wonder if this is a common problem?

If you don't mind me asking what was the power difference on the dyno between the 2 oil pumps assuming there were no other changes?

[DaveMcLain]

I just ran into a similar situation with a 383 Chevy engine that I assembled for a customer. It came in all put together but he had me take it all back apart, check it out, put it back together and test it on the dyno. I saw that the engine had a Melling M55HV pump with I think a purple spring. I KNEW I should have changed it because a stock pump is perfectly adequate in one of these engines with proper bearing clearances. Sure enough on the dyno that thing had 100lbs of hot oil pressure and it would idle with 70 or so which I felt was just too much. With the engine still on the dyno I dropped the pan and put in a stock out of the box Melling M55 pump which now gives about 70lbs hot pressure when rev-ed up which is more than enough. I wonder if this is a common problem?

Not common imo, my high volume pump has a high pressure spring in it and it gives 75 psi cold at idle, 65 hot and 40 hot at idle. Bearing clearances are .0023 rods and .0025 mains.

Maybe something is restricted somewhere.

The engine was put together with .0025 main and .002 rod bearing clearances and has a hydraulic roller cam in a factory roller block. The engine came into the shop with the short block put together but the owner(who had put it together) wanted me to take it apart and make sure everything was ok. The engine had .0045 main and .003 rod bearing clearances along with oil rings that were not installed correctly. I think that what happened was that when the engine was originally built it must have had low pressure so someone put in an HV pump along with a high pressure spring. With normal clearances it didn't need near that much pump volume so at idle it was very high and probably up against the relief then when rev'ed up the pressure could only go higher and it would hold 100psi at any engine speed over about 4500rpm.

I didn't have time to dyno test the engine after the pump swap but it would have been interesting. I just started it, ran it for about 30 minutes under load to check for leaks etc and considered it done. I doubt there would have been a significant difference in the over all engine power I just wanted to try to keep the distributor gear to a minimum on the SADI core camshaft.

Also this was running with Valvoline VR1 20W-50 oil which is what most of these jet boat guys use around here maybe a 10W-30 would have been better but I don't think that would make much difference once the oil got fully warmed up anyway.

[racear2865]

20W-50 is extremely high viscosity for a cold water boat engine. How hot does this engine get. Most of them never see 160*. When you removed the HV oil pump and installed the M55 oil pump, did you check the screen height. A HV pump is about .250 longer and moves the pump screen down 1/4 in .If you installed the stock pump, then the screen goes up 1/4 inch. With cold oil and 50w, the pressure will be high.
reed

[DaveMcLain]

20W-50 is extremely high viscosity for a cold water boat engine. How hot does this engine get. Most of them never see 160*. When you removed the HV oil pump and installed the M55 oil pump, did you check the screen height. A HV pump is about .250 longer and moves the pump screen down 1/4 in .If you installed the stock pump, then the screen goes up 1/4 inch. With cold oil and 50w, the pressure will be high.
reed

From what I could tell the screen seemed to be about the right distance from the bottom of the pan. Remember that while the engine may only have a coolant temperature of 160 the oil can be 100 degrees hotter due to the loading. I wasn't quoting the cold pressure either that was after about 45 minutes of moderate load running and about 15 pulls worth of dyno work.

[cadamzak]

Besides parasitic drag, what other problems am I going to have if we try running this engine the way it is?

[David Redszus]

Besides parasitic drag, what other problems am I going to have if we try running this engine the way it is?

Excessively high oil pressure will increase pumping losses. But there is much larger problem with excesive oil pressure; oil aeration. When the pressure relief valve opens, oil is returned to the sump in a very aerated form. This reduces the oil density, reduces the thermal transfer properties of the oil and becomes a form of oil starvation. Even if the oil pressure is maintained.

It has become standard practice to run oil pressure readings into a data logger and plot against engine rpm. The oil pressure should increase linearly with rpm. When the pressure curve flattens, the oil relief valve is dumping oil and the aeration process has begun.

Excessively high oil pressure has never helped an engine. Using the right oil viscosity at the right temperature is the life blood of an engine.

[Kevin Johnson]

Besides parasitic drag, what other problems am I going to have if we try running this engine the way it is?

Excessively high oil pressure will increase pumping losses. But there is much larger problem with excesive oil pressure; oil aeration. When the pressure relief valve opens, oil is returned to the sump in a very aerated form. This reduces the oil density, reduces the thermal transfer properties of the oil and becomes a form of oil starvation. Even if the oil pressure is maintained.

It has become standard practice to run oil pressure readings into a data logger and plot against engine rpm. The oil pressure should increase linearly with rpm. When the pressure curve flattens, the oil relief valve is dumping oil and the aeration process has begun.

Excessively high oil pressure has never helped an engine. Using the right oil viscosity at the right temperature is the life blood of an engine.

If you use an internal bypass, any free air from the sump has a longer and greater opportunity to enter solution. When the air enters solution in the oil the oil will behave as a fluid rather than an emulsion or mixture of air bubbles and oil -- providing that the pressure on that system is continued sufficient to keep the dissolved quantity of air in solution.

Paraffinic oil base stocks will accept about 9% by volume, per bar pressure. So every 15 psi of pressure allows another 9% to dissolve. This also means, as an aside, that the resting oil probably already has 9% air dissolved into it.

The problem is that there is a certain bubble diameter range, larger than which pretty much assures that free air bubbles will be circulating in the system which is very bad. When the pump bypasses internally, larger bubbles are pulverized into smaller ones and these can enter solution much more easily. If you need the link to an SAE paper from Ford discussing this, let me know.

With the Porsche 928, Porsche engineers used an overdriven massive crescent pump with internal bypass to take advantage of this.

[CNC BLOCKS]

Most of my circle track engines I use a 10553 pump and the ones with a little more clearance and .875 or .904 lifters I use the 10552 oil pump 10% more volume.

On the Honda rod 283 mains I use the 10553 and drill another hole in the cover to bypass the oil so the oil pressure does not spike.

When oil bypasses in the pump it does not back in the sump as mentioned earlier it stays in the pump until its moved out of the pump.

[DaveMcLain]

Besides parasitic drag, what other problems am I going to have if we try running this engine the way it is?

It puts a lot of extra load onto the cam/distributor gear.

[CNC BLOCKS]

Besides parasitic drag, what other problems am I going to have if we try running this engine the way it is?

More oil temps as well.