If it is a rear sump and has anything smaller than a 7/8 pickup tube the pump is cavitating.

 

Agreed. Did you say what RPM this occurs at? I have found once I started turning 8k and above, I had the same deal. I fixed with brute force by going to external oil pump.

 

What Stuska1 said, but if it makes good oil pressure after the oil is warm, you may try a thinner oil and see if things improve.
Less viscous oil will flow more freely, and be less likely to cavitate.

And, as Jim said, see if you can find a bigger pickup. Most are 3/4".

Good Luck

 

Why in the world would he be using 20/50 oil.

 

I am not sure what the pickup size is. It is the b&b stefs steel pan that jegs sold under their name.

 

It seems to occur at anything over 5000rpm

 

He is going to try and use some 10/40 and see if that helps it out. I was thinking it was cavitation or sucking the pan dry but didn’t think it would happen so fast

 

My 363 had oil pressure issues above 7k rpm. Dropped like a rock from 75 to 45 between 7k and 8k.
Oil was Driven BR40 10x40 break in oil on the dyno. I'm sure it would have done it with other oil as well.
This was with a 3/4" pick up and a high volume pump.
After going to a 7/8" pick up and standard volume pump, the issue disappeared.

 

They don’t sell the pan anymore so I am not sure if it’s 3/4 or 7/8, from what I remember it was larger.

would a lighter weight oil help? Worth a try?

 

would a lighter weight oil help? Worth a try?

Cavitation is when the pump tries to draw oil up the pickup, but there's too much resistance to flow, so the pump pulls a vacuum and bubbles/vacuum space is created. These rapidly collapse and cause issue.

Using an oil that will flow more easily will help avoid creating that vacuum from thick oil not being able to flow to the pump quickly enough.

You're trying to get oil to the pump and keep it fed. A larger pickup and thinner oil will help.
I used a larger pickup to help feed and switched to a standard volume pump to reduce demand.

Maybe Jim (Stuska1) can also add his input as well. He is the one who told me to go to a bigger pickup after running my engine on his dyno and seeing the pressure drop off. There were ZERO 7/8" pickups available for a front sump, so one needed to be fabricated. I'm sure a rear sump is more sensitive to diameter, as it's far longer. The longer a pipe, the more resistive it is to flow... especially with thick liquids.

 

I understand what you are saying. I wonder if anyone makes a 7/8 diameter pickup for a rear sump pan. A Quick Look at summit only list 3/4 as the largest

 

Is this just when the car is stationary? Does it hold good pressure when going down the road?

 

He first noticed it while going down the road, so it does it sitting still or moving. It doesn’t do it at normal cruising rpm of 2500 rpm or so, I am not exactly sure when it starts but from what I say 4500-5000 if you hold it there.

 

I definitely would try the 10w40 and possibly 10w30. Why would a SBF need that much pressure?

 

It’s a street car and for whatever reason he feels more comfortable with more pressure is what he tells me. Long trips with hot oil and 20/50 he says it’s 30psi at idle. He is worried with 10/30 it will be too low

 

It's possible that he is creating an issue where there is none.

On a sbf, I'm happy with ~15# hot idle.

 

I sure wouldn’t be. I would be happy with 30psi at thoroughly hot idle in traffic though.

 

I have a similair sbf with same clearances. I'm running a moroso rear pan/pickup with melling hv pump. Now I'm wondering what pickup diameter is? I don't have the pressure drop that you are seeing. My setup will run the pan dry just before the end of the 1/4 because of poor head drain back. Engine is shifted 7-7200 and stays high on rpms with a loose convertor. I added an extra quart of oil and problem went away. Next time I have the engine out, I will be adding external head drains to pan.

I have the pump set to 65psi now. I ran 20/50 in the past. Currently running Driven GP1 15/40 for the last 3 years. I am very happy with the quality of that oil.

 

He is going to try some 10/30 VR1 as he can get that local and see what happens

 

He did confirm the pickup is .75

 

A 3/4" pick up is plenty for that small engine but with those clearances there's no way I'd be using any more than a 30wt oil -or- a HV pump. I'd recommend Driven GP1 10w30 but the VR1 is a good oil.
I wouldn't lose any sleep over idle oil pressure, even 10-15#, as long as it reacts to rpm and has decent pressure once rpm comes up. You might have a pick-up to pan clearance issue if it starts dropping with more rpm.

 

I know he shot for the pan clearance to be set 3/8 to 7/16

 

Jack the front up 6” and see if repeats the problem.

 

You think it may be sucking the pan empty? System has 7 qts

 

You said he added another quart and that made no difference, so no. I agree with the others who point to pickup restriction with that thick oil. I’d want to see what it does with 10W30 or 10W40 first.

 

He is supposed to be doing that today

 

Also another thing I want to mention is he has a moroso vacuum pump on the engine and it pulls about 15”. At what point will that have an effect on the pumps ability to pull oil up the pick up tube? What is the most crankcase vacuum recommended on a wet sump engine like this? I pull 12” with mine.

 

An oil pump in a car is a suction pump on the intake side, and a pressure pump on the output.
If you draw TOO MUCH vacuum in the engine, there will be insufficient atmospheric pressure to feed oil up the pickup tube.

A suction pump relies on a pressure differential to draw on the liquid. It creates a vacuum, and atmospheric pressure (14.7 psi... close to 30inHg) pushes the fluid through the tube. If you're drawing 15inHg out of the engine, there's only 15ihHg to feed the suction side of the oil pump.

As Stuska1 said, if you're drawing enough vacuum to adversely affect oil pressure, you're drawing too much.
Best not to get too greedy there.

 

That just makes it harder to pull oil into the pump, you should unhook the pump and try it. The vac. pump will just enhance the need for a bigger pick up tube. If Vac pump affects oil pressure you are running too much vac.

 

Jim have you seen that?

I am also running a vac pump. Had it set to 12" with no issues. Everything I was told, says the vac will not effect the actual oiling inside the engine since the pump and everything else are inside the same atmosphere?? The gauge will read about 1psi less at every 2" of vac with the same oiling.

 

It hasn't been mentioned but what filter? Some are just inherently more restrictive than others.

And does he have room for the bigger F-700 size filter, like a Baldwin BT-251? They have a slightly larger micron rating but the filter element is about twice the size of a regular filter. They are good for several pounds of pressure.