Jacko3 wrote:My dear C-Kwik:
Where do I begin?
1. What does big block, small block, medium block have to do with heat dissipation and conduction? Does cast iron decide where it wants to take heat from or where it wants to let heat go or does the engines aluminium walls make that decision? I doubt it.
I apologize, I should have elaborated. A motor's expulsion of heat is quite complex. The point of convieving the motor as a solid block was to simplyify the discussion. We could go on and on about how heat leaves through the cooling system, exhaust system and through radiating and convecting heat out of it's many parts and into many mediums, but that would be largely irrelevant. Even given the fact that the crank itself can only transfer so much heat through it's relatively narrow cross sections.
Jacko3 wrote:2. When you drop of your car after driving for say, about 30 minutes, and you open up the hood, do you feel some heat or not, inspite of the very good cooling system you have in your car? And you really feel any metal component of the car does not feel that same heat? Please explain to us more about this anomalous explanation? Invariably, you are saying that the flywheel is somewhat insulated from the very same heat anyone can feel when they open the hood of a car that has recently been driven.
There are two things you appear to be ignoring. First of all, when an engine is running, the radiator fan will kick on as it needs to. And while the car moves, it inevitably gets a stream of air flowing through the radiator. Both of which essentially pumps hot air throughout the engine compartment. So, this combined with radiated heat, will combine to make parts inside the engine compartment warm or hot despite being in direct contact. But the temperature of this air is likely lower than the temperature of the water in the cooling system by a small percent.
When you shut down the motor, radiant heat will of course heat up parts on the engine compartment as it has been doing even while the car is running.
But what you fail to miss here is that even with radiant heat and heat passed through convection, the temperature of the flywheel can only get as high as the temperature of the sources of heat. Due to the thermal barriers that exist, this temperature will likely be lower, but for argument's sake, lets say that it is the same. Assuming the cooling system is doing it's job correctly, then you're talking about a flywheel temperature of about 195 to 220 degrees F. The effect on the flywheel and clutch from heat sourced from the engine, regardless of if it is through conduction, convection or radiation, is not going to be high enough to become a major source of slippage or breakdown of the chemical composition of the clutch's materials.
This is actually a good time to bring up some facts about asbestos. First, it is not flammable. Period (
http://www.btinternet.com/~ibas/lka_prop.htm). It does not oxidize at high temperature. In fact, it decomposes at high temperature. The temperature may vary with the type of asbestos involved, but we are talking 1,000 plus degrees Celsius here. Since we've been using Farhenheit more, that equates to 1,832 degrees Farhenheit. Turbo manifolds, which tend to run very hot, typically reach about 1,400 degrees Farhenheit. Think about that.
Jacko3 wrote:3. Engine is made up of some aluminium, and fly wheel is made up of Iron. Both are metals and so both will get heated at any rate. Engine will give away heat faster than Flywheel and will absorb heat faster than flywheel. Thus, a flywheel is a sitting heat sink and duck. Btw, no one ever uses the term heating dam. We call it heat sink or heat dump in the world of engineering. A refrigerator compressor is a classic heat sink.
Once the flywheel reaches a certain temperature, (which will not be higher than the temperature of the source), it will reject heat. Think of it this way. If you heat up your oven to 500 degrees, and stick something in it, that something will not ever become a higher temperature than the air around it.
Jacko3 wrote:4. Primary source of heat to flywheel is by convection and secondarily by conduction. Thus my earlier focus on convection. Why? The surface area of the crankshaft in contact with the any surface area of the flywheel is very small. But the surface area of the flywheel in contact with the heated air from the engine wall is in totality of the area of the flywheel. So the crankshaft could not possibly heat up the flywheel as effectively as you have erroneously described. The main heat to the flywheel comes from the heat accumulated or developed on the outside walls of the engine that is being transmitted by convection or air to the walls of the flywheel and other parts of the car. When you open up the hood of your car after driving, the heat you experience is by convection. Your flywheel experiences that same heat. There is no insulation b/w the engine wall and the flywheel that is effective enough to reduce the heat. If you know of one, please tell me.
Lets just assume your are right about where the heat in a flywheel is generated from (aside from and frictional heat induced by clutch slip). As I said, since the temperature will be no higher than the temperature of the air around it, than in order to bring the clutch and flywheel temperature up even more is to cause it to become a source of heat by slipping the clutch. This, more than any other source has the potential to heat the flywheel and clutch up to a temperature where things start to go awry. But as I stated before, if you are driving correctly and everything is working properly, this should never happen. And if you do slip the clutch a bit, and generate some heat, it will occur at the contact surfaces. Then, it will start to spread into the surrounding materials. Some will go into the clutch disc (many organic disc manufacturers embed strands of metal into the disc to help pull heat away from the surface of the disc quicker). Some will go into the pressure plate's disc, and some will go to the flywheel. But since the flywheel has the greatest mass, the tendency will be that most of the heat will go there as the temperature increase from a given amount of energy will be small.
Jacko3 wrote:5. Better materials are absolute. What you are talking about is individual comfort. Yes, some people may prefer OEM clutches to ceramic based clutches which might chatter a little more. Certainly some people will be comfortable with some types of materials than others. A better material is simply one that can dissipate heat fast and absorb heat less. This charateristics is absolute. I really wouldn't like to go into the theories of heat absorption. There is no need for it.
How can it be absolute. Better, in that of itself is a term that describes an opinion. An opinion is largely or sometimes wholly based on personal choices. So better materials can't be absolute unless the word better is qualified. If you are looking for a clutch that has a higher coefficient of friction, then yes, there is a better material than the OE materials. If you want a clutch that lasts longer, there is a better material than OE and even metallic clutches. If you want a clutch that can hold a little better than stock without sacrificing comfort, yes, there is a better clutch for that too. It's all a matter of perspective.
Jacko3 wrote:6. Ceramics have been known to be great at this heat characteristics. They also double as insulators as well. Haven't you heard that ceramic breaks don't wear out as fast as the asbestos brakes? why do you think this is so? So you think, the after market guys are just deceiving the buyers of ceramic brakes? I just explained why, in my write up above. The reason they have ceramic materials is because it is a good insulator of heat because it does not absorb heat very quickly. And when it does, it dissipates the heat very fast. the same ceramic materials are used as heat shields in NASA's space crafts. Ceramics don't yield to expansion as quickly as asbestos do.
No material can be a good insulator and good conductor of heat at the same time. They are inversely proportional traits. Readup:
http://theory.uwinnipeg.ca/mod_tech/node75.html
What asbestos brakes? I doubt very many brakes contain any asbestos now or even for some time. Bear in mind that ceramic brakes tend to have a soft metal (such as copper embedded to provide an adequate level of heat transfer).
Jacko3 wrote:7. Thermal expansion naturally reduces the tendency of a material to maintain its lateral load when coupled with another material with a different coefficient of friction and atomic make up. Another simple reason for this is that particle sizes and arrangement, of both the flywheel cast iron and the asbestos, on the clutch, are different. Thus, heat will render the particles of the least packed atoms (clutch particles), more prone to disintegration than the particles of the most packed atoms (flywheel). The physics you describe only aids in speeding up that process. This issue is first and foremost a material science issue and not a physics issue. You can throw in all the lateral load you want, if the material is not stable under increasing levels of heat conduction, your laterally loaded material will fail. Every material is subject to the effects of heat and its properties. Load only speeds up the detiororation process, and it is the job of the engineers to find a material that will withstand the lateral load for a specific amount of time, as dictated by the manufacturer. Thus, material science tests are always crucial, and conducted, in any part of a machinery that will experience some type of heat absorption, and yet accept some load.
Lets assume this is true. Are you saying that engineers are using unstable components that will fail in our cars? Not likely. Any effect this might have would be minimal/negligible. Your last line in this paragraph indirectly asserts what I am saying here.
Jacko3 wrote:8. Engineers are bound moreso than any other set of factors, by safety and cost. Any engineering feat that fails to live up to safety and cost, is almost always shelved, regardless of how good the technology might be. For example, it has taken forever for run flat tires to make it to main stream auto world. Well, the safety issues of run flats are pretty good an obvious, but the costs still remain prohibitive. So, run flats are only found in cars associated with thew wealthy who have an income inelasticities to any good or product they demand. Asbestos in most clutch systems has been shown to be relatively safe and inexpensive, ceteris paribus. So, why mess with it if it ain't broke? Asbestos is so cheap and so convenient that it took law suits to remove them from paint and roofing materials in homes in the US. Yet, they are still popular outside the US.
Engineers are bound by the requirements put on them by the company they work for. Safety and cost are most certainly something most companies will put at least some attention on and in most cases, a lot of attention on. But a product still has to reasonably perform to be successful. Run flat tires are typically only used by cars that don't have room for a spare. Many of these are high end sports cars that actually perform quite well. The Corvettes and even the upcoming GT-R are examples...
Jacko3 wrote:9. You will need a thermal boundary once the clutch smell occurs, only for a short duration dissipation of heat built up between the clutch and the flywheel. That heat build up is not from the interaction of the flywheel and clutch. Rather, it is from the heat absorbed by both the flywheel and the clutch that slowly degenerates the clutch, since the clutch itself has less packed atoms than the flywheel.
How can a level of heat that would cause one to approach a point where the clutch smells occur from any source other than the frictional interaction of the clutch system? Heat always transfers from hot to cold. When you put two objects with different temperatures together, the hot one begins to cool as it transfers heat to the cold object. The cold object begins to go up in temperature. Eventually, both objects will equalize in temperature and then heat transfer stops. Even if one of the objects continually emits heat at a certain temperature, then the colder object will increase in themperature until it becomes the same temperature. And again, the heat transfer stops. This means that unless there is a hotter temperature source added to the equation, the temperature of either object can not increase. Ther must be another source of heat energy available to increase the temperature of the clutch and flywheel and pressure plate higher than that of the engine. It's a relatively simple concept. You can argue tooth and nail here, but you can't bend the laws of physics.
Jacko3 wrote:10. I am fully aware of driving hard and abusig a car.
If you say so...
