Originally Posted By: BuickGN
Originally Posted By: CATERHAM
Originally Posted By: Junior
Originally Posted By: BuickGN
I guess what I'm looking for is an admission that higher power outputs regardless of temperature require higher viscosities to keep things separated.
In general for a given bearing, higher loading or lower RPM will require a higher viscosity. But the viscosity selected has to take into account the actual operational conditions and physical size of the bearing. For example, and F1 engine has a high specific power output per liter but I have read they use low viscosity oils. Of course they spin 19,000 rpm and are not a fair comparison when speaking in terms of passenger car engines.
The point is, viscosity is selected based on the application not just the power output alone.
You don't know what they use for a fact so don't post opinions as such.
I get condemned for posting my "race engine" results in the GN with my stock clearances and production parts using a thick oil to survive yet it's ok for you guys to mention Top Fuel and F1. And consider that valide. Here's a question, how much torque do F1 cars make?? You may find you answer in there.
BuickGN, my mentioning something I read is not stating it as fact. This is a discussion board, not a technical paper where I am required to credit my source. Your arguments are based on your experiences and the data you collected. You studied the data and developed your own conclusions. Like it or not, that is your opinion. And, in my post I did mention the F1 is not a fair comparison to typical automotive.
The funny thing is, I agree with you that if you take a stock engine and increase the power it produces, you probably need to increase the viscosity.
Where I don't agree with you is where you try to use power and torque to mean the same thing. Power is a calculated value based on (in terms of an internal combustion engine) two measurable values, speed and torque. You can have two engines that make the exact same power but operate at very different speeds and have very different torque curves.
In answering your torque question, lets take the example of doubling the power of an engine. There are two basic ways to accomplish this. 1)keep the RPM constant and double the torque. 2) keep the torque constant and double the speed. In both cases the overall power output has been doubled.
In example 1, Yes you are most likely going to have to increase the viscosity because that torque relates to higher loading on the bearings. This is consistent with what I originally stated about increased load requires increased viscosity.
In example 2, the torque load did not increase so we do not necessarily need to increase the viscosity because the increased bearing speed is going to increase the size of the hydrodynamic wedge in the bearing. Increased speed does present it's own challenges which I admit I am ignoring to keep this example simple.
Like I said before, viscosity is selected for the application. A blanket statement of needing a higher viscosity for higher power output is not correct without knowing the operating conditions and engine design. And to repeat myself, there are formulas and tables to calculate the required viscosity for a journal bearing based on the speed, load, bearing design and desired hydrodynamic wedge thickness. It's not a guessing game. It is a compromise to select a lubricant the will have viscosity characteristics that will work across the expected operational profile of the bearing.
Originally Posted By: CATERHAM
Originally Posted By: Junior
Originally Posted By: BuickGN
I guess what I'm looking for is an admission that higher power outputs regardless of temperature require higher viscosities to keep things separated.
In general for a given bearing, higher loading or lower RPM will require a higher viscosity. But the viscosity selected has to take into account the actual operational conditions and physical size of the bearing. For example, and F1 engine has a high specific power output per liter but I have read they use low viscosity oils. Of course they spin 19,000 rpm and are not a fair comparison when speaking in terms of passenger car engines.
The point is, viscosity is selected based on the application not just the power output alone.
You don't know what they use for a fact so don't post opinions as such.
I get condemned for posting my "race engine" results in the GN with my stock clearances and production parts using a thick oil to survive yet it's ok for you guys to mention Top Fuel and F1. And consider that valide. Here's a question, how much torque do F1 cars make?? You may find you answer in there.
BuickGN, my mentioning something I read is not stating it as fact. This is a discussion board, not a technical paper where I am required to credit my source. Your arguments are based on your experiences and the data you collected. You studied the data and developed your own conclusions. Like it or not, that is your opinion. And, in my post I did mention the F1 is not a fair comparison to typical automotive.
The funny thing is, I agree with you that if you take a stock engine and increase the power it produces, you probably need to increase the viscosity.
Where I don't agree with you is where you try to use power and torque to mean the same thing. Power is a calculated value based on (in terms of an internal combustion engine) two measurable values, speed and torque. You can have two engines that make the exact same power but operate at very different speeds and have very different torque curves.
In answering your torque question, lets take the example of doubling the power of an engine. There are two basic ways to accomplish this. 1)keep the RPM constant and double the torque. 2) keep the torque constant and double the speed. In both cases the overall power output has been doubled.
In example 1, Yes you are most likely going to have to increase the viscosity because that torque relates to higher loading on the bearings. This is consistent with what I originally stated about increased load requires increased viscosity.
In example 2, the torque load did not increase so we do not necessarily need to increase the viscosity because the increased bearing speed is going to increase the size of the hydrodynamic wedge in the bearing. Increased speed does present it's own challenges which I admit I am ignoring to keep this example simple.
Like I said before, viscosity is selected for the application. A blanket statement of needing a higher viscosity for higher power output is not correct without knowing the operating conditions and engine design. And to repeat myself, there are formulas and tables to calculate the required viscosity for a journal bearing based on the speed, load, bearing design and desired hydrodynamic wedge thickness. It's not a guessing game. It is a compromise to select a lubricant the will have viscosity characteristics that will work across the expected operational profile of the bearing.
