Flow and RPM
- Thread starter Fbear
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I'd wager more flow, because of higher oil pressure at higher RPM. But I wouldn't say the increase in flow is a linear function of the oil pressure.
Pressure goes up, all else is equal, means there is more flow.
But, on the HL at least there is a "waste gate" between the pump and filter, so once pressure hits a certain point it levels from there upward.
But, on the HL at least there is a "waste gate" between the pump and filter, so once pressure hits a certain point it levels from there upward.
You oil pump displaces oil with each revolution, so as rpm's increase, so does flow.
The pump does not produce pressure. Pressure is produced by resistance to the flow from the pump.
There will be a some loss of efficiency as resistance (oil pressure) increases, and at some point a by-pass vale will open to relive pressure.
But by and large flow increases with rpm.
The pump does not produce pressure. Pressure is produced by resistance to the flow from the pump.
There will be a some loss of efficiency as resistance (oil pressure) increases, and at some point a by-pass vale will open to relive pressure.
But by and large flow increases with rpm.
Read "Motor Oil by AE Haas".
The viscosity of the oil affects the resistance to flow and thus the back pressure.
Ideally at running temperature, the oil should be chosen to have a low enough viscosity so that the back-pressure caused by resistance to flow just reaches the relief valve pressure setting at the highest normal RPM the engine sees. Choosing the oil to do this will provide the maximum flow rate at highest normal RPM, and thus provide the maximum amount of cooling of the surfaces the oil flows through, by the oil cooling those parts.
As long as the oil is not so thin that it allows metal to metal contact, using a thin oil improves heat removal by preventing the pressure relief valve from opening at lower than maximum normal RPM. This is why high revving engines such as F1 cars use light weight oils.
One thing to keep in mind is that many older engine designs have bearing surfaces that require a 30 weight upper number or greater to prevent metal to metal contact. Also keep in mind that if the oil becomes too thin to prevent metal to metal contact, most oils have additives to act as a secondary barrier (last resort) to prevent metal to metal contact. This is why some older engines will wear out certain surfaces like cam lobes on solid lifters if the oil has too little amount of these types of additives such as ZDDP.
The amount of additives are usually expressed in PPM (parts per million by weight) and 1000 PPM = 0.1 percent.
Unfortunately ZDDP (a good anti wear additive) can poison a catalytic converter. Therefore the amount of ZDDP in modern oils has been lowered to increase the life of catalytic converters. This can result in older engines that require the higher old amounts of ZPPP being damaged if modern oils are used in them.
The viscosity of the oil affects the resistance to flow and thus the back pressure.
Ideally at running temperature, the oil should be chosen to have a low enough viscosity so that the back-pressure caused by resistance to flow just reaches the relief valve pressure setting at the highest normal RPM the engine sees. Choosing the oil to do this will provide the maximum flow rate at highest normal RPM, and thus provide the maximum amount of cooling of the surfaces the oil flows through, by the oil cooling those parts.
As long as the oil is not so thin that it allows metal to metal contact, using a thin oil improves heat removal by preventing the pressure relief valve from opening at lower than maximum normal RPM. This is why high revving engines such as F1 cars use light weight oils.
One thing to keep in mind is that many older engine designs have bearing surfaces that require a 30 weight upper number or greater to prevent metal to metal contact. Also keep in mind that if the oil becomes too thin to prevent metal to metal contact, most oils have additives to act as a secondary barrier (last resort) to prevent metal to metal contact. This is why some older engines will wear out certain surfaces like cam lobes on solid lifters if the oil has too little amount of these types of additives such as ZDDP.
The amount of additives are usually expressed in PPM (parts per million by weight) and 1000 PPM = 0.1 percent.
Unfortunately ZDDP (a good anti wear additive) can poison a catalytic converter. Therefore the amount of ZDDP in modern oils has been lowered to increase the life of catalytic converters. This can result in older engines that require the higher old amounts of ZPPP being damaged if modern oils are used in them.
Last edited:
Pressure is a restriction to flow.
Originally Posted By: JimPghPA
Read "Motor Oil by AE Haas".
The viscosity of the oil affects the resistance to flow and thus the back pressure.
Ideally at running temperature, the oil should be chosen to have a low enough viscosity so that the back-pressure caused by resistance to flow just reaches the relief valve pressure setting at the highest normal RPM the engine sees. Choosing the oil to do this will provide the maximum flow rate at highest normal RPM, and thus provide the maximum amount of cooling of the surfaces the oil flows through, by the oil cooling those parts.
As long as the oil is not so thin that it allows metal to metal contact, using a thin oil improves heat removal by preventing the pressure relief valve from opening at lower than maximum normal RPM. This is why high revving engines such as F1 cars use light weight oils.
One thing to keep in mind is that many older engine designs have bearing surfaces that require a 30 weight upper number or greater to prevent metal to metal contact. Also keep in mind that if the oil becomes too thin to prevent metal to metal contact, most oils have additives to act as a secondary barrier (last resort) to prevent metal to metal contact. This is why some older engines will wear out certain surfaces like cam lobes on solid lifters if the oil has too little amount of these types of additives such as ZDDP.
The amount of additives are usually expressed in PPM (parts per million by weight) and 1000 PPM = 0.1 percent.
Unfortunately ZDDP (a good anti wear additive) can poison a catalytic converter. Therefore the amount of ZDDP in modern oils has been lowered to increase the life of catalytic converters. This can result in older engines that require the higher old amounts of ZPPP being damaged if modern oils are used in them.
Do you think zinc protects soft metals ? Babbit and pistons, copper, brass etc ?
Read "Motor Oil by AE Haas".
The viscosity of the oil affects the resistance to flow and thus the back pressure.
Ideally at running temperature, the oil should be chosen to have a low enough viscosity so that the back-pressure caused by resistance to flow just reaches the relief valve pressure setting at the highest normal RPM the engine sees. Choosing the oil to do this will provide the maximum flow rate at highest normal RPM, and thus provide the maximum amount of cooling of the surfaces the oil flows through, by the oil cooling those parts.
As long as the oil is not so thin that it allows metal to metal contact, using a thin oil improves heat removal by preventing the pressure relief valve from opening at lower than maximum normal RPM. This is why high revving engines such as F1 cars use light weight oils.
One thing to keep in mind is that many older engine designs have bearing surfaces that require a 30 weight upper number or greater to prevent metal to metal contact. Also keep in mind that if the oil becomes too thin to prevent metal to metal contact, most oils have additives to act as a secondary barrier (last resort) to prevent metal to metal contact. This is why some older engines will wear out certain surfaces like cam lobes on solid lifters if the oil has too little amount of these types of additives such as ZDDP.
The amount of additives are usually expressed in PPM (parts per million by weight) and 1000 PPM = 0.1 percent.
Unfortunately ZDDP (a good anti wear additive) can poison a catalytic converter. Therefore the amount of ZDDP in modern oils has been lowered to increase the life of catalytic converters. This can result in older engines that require the higher old amounts of ZPPP being damaged if modern oils are used in them.
Do you think zinc protects soft metals ? Babbit and pistons, copper, brass etc ?
Originally Posted By: Fbear
Does oil flow rate GPM change with RPM or is it the same once the car/truck is up to temp regardless if it's at 1,000 rpm or say 6,000 rpm?
For MOST engines, it varies with RPM only at low RPM. As the oil pump spins faster, it pumps more oil. As more oil tries to squirt out the various clearances in all the bearings, lifters, squirt holes and other gadgets, the pressure goes up. At some RPM, the pressure will exceed the pressure regulator setting, and it will start to dump excess oil pumped by the pump back into the pan before it goes through the engine. From then on as RPM continues to increase, flow through the engine remains almost constant. At some RPM, the flow of the oil pump may exceed the ability of the relief valve to vent it, and then pressure will start up again. But I've never seen that happen personally, even with high-volume oil pumps. For example, my 440's both hit their pressure relief points by 2000 RPM, and the oil pressure doesn't change as you go up through 3000, 4000, and 5000 RPM (although a 440 spends VERY little time at 5k, unless its built to deliver on the high side of 600 RW horsepower, which mine aren't.)
Does oil flow rate GPM change with RPM or is it the same once the car/truck is up to temp regardless if it's at 1,000 rpm or say 6,000 rpm?
For MOST engines, it varies with RPM only at low RPM. As the oil pump spins faster, it pumps more oil. As more oil tries to squirt out the various clearances in all the bearings, lifters, squirt holes and other gadgets, the pressure goes up. At some RPM, the pressure will exceed the pressure regulator setting, and it will start to dump excess oil pumped by the pump back into the pan before it goes through the engine. From then on as RPM continues to increase, flow through the engine remains almost constant. At some RPM, the flow of the oil pump may exceed the ability of the relief valve to vent it, and then pressure will start up again. But I've never seen that happen personally, even with high-volume oil pumps. For example, my 440's both hit their pressure relief points by 2000 RPM, and the oil pressure doesn't change as you go up through 3000, 4000, and 5000 RPM (although a 440 spends VERY little time at 5k, unless its built to deliver on the high side of 600 RW horsepower, which mine aren't.)
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Originally Posted By: Steve S
Pressure is a restriction to flow.
Pressure is the expression of flow through a restriction.
Pressure is a restriction to flow.
Pressure is the expression of flow through a restriction.
Originally Posted By: Gary Allan
Originally Posted By: Steve S
Pressure is a restriction to flow.
Pressure is the expression of flow through a restriction.
Originally Posted By: Steve S
Pressure is a restriction to flow.
Pressure is the expression of flow through a restriction.
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