Crankcase vacuum question.

[67 Satellite]

http://www.jegs.com/p/Moroso/745524/10002/-1 Try this link. Hope it works. When you see the prices you'll see why I wanted to try this the "cheap" way.

[kamesama980]

Originally Posted by 67 Satellite

Assuming you have a wet sump oil system,the oil pressure won't be effected at all. The inlet side of the oil pump is in the same vacuum as the outlet side,it will just pump oil from point A to boint B.If it were pumping oil to the outside of the engine then it would have to fight the vacuum,but within the engine the pressures(or vacuums) on both ends of the flow path are equal.

That aside, oil psi is rpm dependant and at idle, usually more than 15 psi. the hydraulic lifters are going to be limited as to the max pressure but will see full oil pressure up to that point. even if you did pull 14 psi vacuum on them directly, there's still plenty of PSI oil pressure to go especially at 5k rpm

[GasSavers_RoadWarrior]

Good point 67 Satellite, thanks.

Another stray neuron suggested... "Hey whaddabout them oldskool airpumps used for emissions, if modified*, would they pull vacuum?"

*Probably you'd need to plumb/fab up an inlet.

Edit: awesome! They appear to be positive displacement vane pumps, some folks are selling them for crankcase evac duty on drag cars, but advise that the electric ones are not suitable for continuous duty. I'll have to go find a vict..errr donor.

[kamesama980]

Originally Posted by RoadWarrior

Good point 67 Satellite, thanks.

Another stray neuron suggested... "Hey whaddabout them oldskool airpumps used for emissions, if modified*, would they pull vacuum?"

*Probably you'd need to plumb/fab up an inlet.

Edit: awesome! They appear to be positive displacement vane pumps, some folks are selling them for crankcase evac duty on drag cars, but advise that the electric ones are not suitable for continuous duty. I'll have to go find a vict..errr donor.

wonder what the net gain would be? the advantage of letting engine vacuum pull the cc vacuum is no extra drag from it. now you're adding a belt, some bearings, and a pump. on the other hand, they're pretty low displacement and whatnot meant to be seamless incorperation into an existing engine.

[onovakind67]

Originally Posted by 67 Satellite

Assuming you have a wet sump oil system,the oil pressure won't be effected at all. The inlet side of the oil pump is in the same vacuum as the outlet side,it will just pump oil from point A to boint B.If it were pumping oil to the outside of the engine then it would have to fight the vacuum,but within the engine the pressures(or vacuums) on both ends of the flow path are equal.

The oil pump moves oil through the pickup tube by creating a vacuum in the pump. The maximum it can create is about 30"hg, and if there is 20"hg on the inlet of the tube, the flow will be considerably less than if there is 2"hg at the inlet to the pickup tube. It makes no difference where the pump is located.

High vacuum in the crankcase also causes bubbles in the oil at the vapor pressure is reduced.

[ZugyNA]

Originally Posted by onovakind67

The oil pump moves oil through the pickup tube by creating a vacuum in the pump.

I think the vac where the oil is picked up will be the same as it is where it can leak out of the oil galleys...i.e....the rod/mains...valve train? So any effect is canceled out? The slight vac might help the rings seal better and cause less oil to migrate past the valve/crank seals?

[onovakind67]

Originally Posted by ZugyNA

I think the vac where the oil is picked up will be the same as it is where it can leak out of the oil galleys...i.e....the rod/mains...valve train? So any effect is canceled out? The slight vac might help the rings seal better and cause less oil to migrate past the valve/crank seals?

Vacuum is an absolute value. You can do no better than a perfect vacuum, and if there is also a perfect vacuum in the crankcase, what will cause the oil to flow through the pickup tube? The higher the vacuum gets in the crankcase, the harder it is to get oil into the pump.

[GasSavers_RoadWarrior]

Heh, if we were talking "perfect vacuum" we'd have to worry about hot metal evaporating. Pumps create a pressure differential, if they're working under 15psi and can put out 50psi over that, then they will still be able to put out 50psi over 3 or 4 psi ambient conditions. Now you might have issues priming a pump in vacuum conditions, air being "stretchy" as it were, but oil is less so and won't be a problem unless you're running el-cheapo bargain bin oil that boils at 160C under atmospheric pressure, decent 200-220C BP oil shouldn't be a problem at the minor vacuums we're talking about.

[67 Satellite]

Originally Posted by onovakind67

Vacuum is an absolute value. You can do no better than a perfect vacuum, and if there is also a perfect vacuum in the crankcase, what will cause the oil to flow through the pickup tube? The higher the vacuum gets in the crankcase, the harder it is to get oil into the pump.

Back to the original intent for a minute.We're not trying to create an absolute vacuum,just a partial of say 5-10".I'm not trying to crush the oil pan with the atmosphere here,just save a little fuel. According to some dyno reports I've seen posted,there is a point of diminishing return for horsepower improvement at somewhere between 12' to 15". Beyond that increased vacuum produces no more power.

[red91sit]

just throwing it out there, if you do want a mechanical crankcase pump, Mercedes Benz equipped some of their cars with them connected to an electromagnetic clutch. I'm not sure when this turns on or off, or why they used such a complex pcv system, but they have them. I know for sure they are on 1985 380 SE's not sure what else they might come on.