Originally Posted By: OVERKILL
Originally Posted By: CATERHAM
Originally Posted By: OVERKILL
Originally Posted By: Clevy
You gained oil pressure by reducing volume of flow.
First off you need to determine max oil temp when driving hard. Then take that temp and look up minimum oil pressure at max temp/rpm.
Now find an oil that will maintain the oil pressure at the max oil temp. That insures adequate pressure and viscosity when the oil is at its hottest.
Then use the thinnest oil you can find that meets your minimum pressure at maximum oil temp.
There is less parasitic loss with thinner oils which means more power to the wheels. Add that to thinner oils allow more volume per pump stroke which means more heat than be removed from the engine faster.
Thin as possible.
As thick as necessary.
A positive displacement oil pump displaces the same amount of oil per revolution if it is TGMO 0w-20 or TWS 10w-60. The volume is constant at a given RPM. Whether some of that oil goes out the bypass or all of it is forced through the engine is determined by the bypass pressure on the release valve. The pressure observed on the gauge is simply indicative as to the level of restriction in the system. And can tell you if the bypass is open or not.
That's true in theory but in practice heavier oil does flow at a reduced rate, even below the by-pass point, than lighter oil particularly when you're comparing a large viscosity difference such as between a 20wt and 60wt oil.
This was discussed in another thread a year or so ago and I don't remember all the technical reasons why but they included oil pump leakage, pick-up pipe diameter and screen size etc.
I would think you'd get greater leakage with a thinner oil than a thicker one....
If pick-up tube diameter and the like plays a role, then engine design, oil pump displacement volume per rotation, pick-up size...etc all play a role too. Which would mean that this varies by application.
Like everything else in an engine, the oil system is highly engineered. It has to be, because it's required to deliver and recover the correct amount of this misbegotten stuff called motor oil to and from all parts of the engine, and do it over a range of temperatures that goes from -40 to 300 F. Over this range of temperature, the oil goes from the consistency of sour cream to milk, so the actual amount of oil flow required by the engine changes proportionally to the viscosity. The oil pump has to be sized and regulated to keep oil pressure within an acceptable range.
The OP is modifying his engine to run at higher speeds, which is increasing the flow requirement to probably more than the pump was sized for, which may be why he is seeing a drop in pressure at max rpm. Or maybe the pump is suffering from cavitation at the inlet. Or maybe the oil is foaming due to high rpm churning, entraining a lot of air, and compressing in the galleries. Or maybe oil is staying in the cylinder head, unable to drain back to the pan because of inadequate crankcase venting, causing the oil pump to suck air. Which of these posible conditions is the cause of the OP's problem? I don't know.
The favorite method of dealing with loss of oil pressure at high rpm is to increase oil pump displacement. But this may make things worse if the problem is with oil drainage. A higher displacement pump that can maintain regulated pressure at high rpm will pull oil out of the pan faster and force more flow through the engine pressure system. But when the oil gets into the drain system, it still has to get back to the pan under the force of gravity, which did not change when the pump displacement was increased. The final result of this could be that the pump draws the level in the pan down quicker than the original, causing the pickup to suck air sooner. This is why I am not an advocate of 70+ psi oil pressures. Like Caterham has said, if you can maintain 50 psi of stable oil pressure at maximum operating speed, be happy.
Originally Posted By: CATERHAM
Originally Posted By: OVERKILL
Originally Posted By: Clevy
You gained oil pressure by reducing volume of flow.
First off you need to determine max oil temp when driving hard. Then take that temp and look up minimum oil pressure at max temp/rpm.
Now find an oil that will maintain the oil pressure at the max oil temp. That insures adequate pressure and viscosity when the oil is at its hottest.
Then use the thinnest oil you can find that meets your minimum pressure at maximum oil temp.
There is less parasitic loss with thinner oils which means more power to the wheels. Add that to thinner oils allow more volume per pump stroke which means more heat than be removed from the engine faster.
Thin as possible.
As thick as necessary.
A positive displacement oil pump displaces the same amount of oil per revolution if it is TGMO 0w-20 or TWS 10w-60. The volume is constant at a given RPM. Whether some of that oil goes out the bypass or all of it is forced through the engine is determined by the bypass pressure on the release valve. The pressure observed on the gauge is simply indicative as to the level of restriction in the system. And can tell you if the bypass is open or not.
That's true in theory but in practice heavier oil does flow at a reduced rate, even below the by-pass point, than lighter oil particularly when you're comparing a large viscosity difference such as between a 20wt and 60wt oil.
This was discussed in another thread a year or so ago and I don't remember all the technical reasons why but they included oil pump leakage, pick-up pipe diameter and screen size etc.
I would think you'd get greater leakage with a thinner oil than a thicker one....
If pick-up tube diameter and the like plays a role, then engine design, oil pump displacement volume per rotation, pick-up size...etc all play a role too. Which would mean that this varies by application.
Like everything else in an engine, the oil system is highly engineered. It has to be, because it's required to deliver and recover the correct amount of this misbegotten stuff called motor oil to and from all parts of the engine, and do it over a range of temperatures that goes from -40 to 300 F. Over this range of temperature, the oil goes from the consistency of sour cream to milk, so the actual amount of oil flow required by the engine changes proportionally to the viscosity. The oil pump has to be sized and regulated to keep oil pressure within an acceptable range.
The OP is modifying his engine to run at higher speeds, which is increasing the flow requirement to probably more than the pump was sized for, which may be why he is seeing a drop in pressure at max rpm. Or maybe the pump is suffering from cavitation at the inlet. Or maybe the oil is foaming due to high rpm churning, entraining a lot of air, and compressing in the galleries. Or maybe oil is staying in the cylinder head, unable to drain back to the pan because of inadequate crankcase venting, causing the oil pump to suck air. Which of these posible conditions is the cause of the OP's problem? I don't know.
The favorite method of dealing with loss of oil pressure at high rpm is to increase oil pump displacement. But this may make things worse if the problem is with oil drainage. A higher displacement pump that can maintain regulated pressure at high rpm will pull oil out of the pan faster and force more flow through the engine pressure system. But when the oil gets into the drain system, it still has to get back to the pan under the force of gravity, which did not change when the pump displacement was increased. The final result of this could be that the pump draws the level in the pan down quicker than the original, causing the pickup to suck air sooner. This is why I am not an advocate of 70+ psi oil pressures. Like Caterham has said, if you can maintain 50 psi of stable oil pressure at maximum operating speed, be happy.
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