[DeepBrainThrombosis]

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.

 

[scott foxwell]

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.

 

[Brad87gt]

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

 

[makinchips]

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

 

[Brad87gt]

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

 

[DeepBrainThrombosis]

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.

 

[Brad87gt]

He is supposed to be doing that today

 

[Brad87gt]

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.

 

[stuska1]

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.

 

[juiced coupe 78]

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.

 

[Brad87gt]

He has tried a few different filters. It is a block mounted 3/4-16 stock ford type filter. But he uses the morose racing filter.

 

[underpsi68]

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.

 

[treyrags]

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

Idle pressure means very little. The engine has almost no load at all. The main thing is the pressure coming up immediately with rpm. But anything over 60 on a SBF is a waste unless it is a very unique combination or use.

 

[stuska1]

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.

If you have a properly designed system, a few lbs isn't going to matter, if you are seeing a 20-30 lb swing you have issues

 

[n2omike]

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.

 

[E.R. Racing]

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.

The oil pump is inside the same atmosphere. They aren't fighting each other.

 

[DeepBrainThrombosis]

The oil pump is inside the same atmosphere. They aren't fighting each other.

I’ve been doing some thinking about this.. actually, the vacuum does make a difference. Not only is it pulling against the oil being sucked up into the pump, thus adding resistance, but it’s sucking on the oil at all outlets on the pressure side as well. When I say all the outlets, of course I mean every rod bearing, every main bearing, every lifter, camshaft bearing. With resistance to pumping on the suction side, and actively sucking out on the pressure side, you will reduce pressure in the entire system.

Consider an experiment - fill a strong container with oil, and install a pressure sensor somewhere below the surface of the oil. Now, pressurize the container and watch the pressure measured at the sensor rise. Now, pull a vacuum on the container and watch the pressure drop.

Back to the oiling system in an engine, the vacuum pulling on the pressure side effectively reduces restriction, thus lowering pressure. Likewise, vacuum pulling on the suction side increases resistance to pumping. It makes total sense that a crankcase under vacuum would see lower oil pressure than a crankcase at atmospheric pressure.

 

[Brad87gt]

He didn’t get around to changing the oil yet, but says he will as soon as possible.

another thing we talked about was that the last time he had the engine out, the only changes made were camshaft. Used the Same lifters. And the oil pan. The oil pan he had before was morose 9” deep pan with nothing in it as far as oil control of any kind. So he put the jegs pan on with a scraper and windage screen and sump protection. Which he thought would be an improvement. Both pickups are 3/4. The jegs pickup is round and funnel shaped. The morose was a rectangular box. So he is thinking the change in pan and pickup being changed is why he is seeing the issue now. With old pan which he has had for several years. Over 10… he said he used to use Pennzoil GT 25/50 racing oil and cannot remember it having this issue. Maybe a coincidence.

 

[n2omike]

The oil pump is inside the same atmosphere. They aren't fighting each other.

The crankcase is not the same atmosphere as the outside.

The outside atmosphere is under a pressure of around 30 inches of water (around 14.7 psi).
The crankcase is under a pressure of around 15 inches of water (around 7.3 psi).

The suction side of the pump creates a vacuum, and the atmosphere pushes the oil up the pickup tube.
The pickup works better with more atmospheric pressure to push the oil up the tube.

Think about it...
Consider trying to drink through a straw. You create a suction on one side, and atmospheric pressure pushes the liquid up to your mouth.

If you're working with full atmospheric pressure, there's a force of 14.7 psi pushing the drink to your mouth... assuming you can create a full vacuum.
If that atmospheric pressure is lowered, there will be less pressure to force the liquid up the straw.
If you pressurized the container past atmospheric, the liquid would flow up all by itself.
Creating a partial vacuum inside the crankcase definitely has a negative effect on the suction side of the oil pump.

 

[E.R. Racing]

The crankcase is not the same atmosphere as the outside.

That is not what I said. The “vacuum” inside the crankcase and the oiling system are both in the same atmosphere.