Omar, Our titanium rods are a lot less than a grand each, but they are not stock. I may have a line on some stock size titanium rods that are collecting dust. Email me if you are interested. Mark Lewis
This is not true. If the coolant is not in the radiator long enough, it will not cool sufficiently. The heat transfer is a function of the surface are and coolant flow. Change those, you change the rate of heat transfer. At some point, the coolant flow/area will provide for optimal heat transfer. Above/Below that you're going to lose the ability to take heat out of the water.
No. The fluid has less time in the radiator to reject heat, but that is matched by reduced time in the engine to gain heat. That means the fluid is cooler and there is more of it, so the engine is cooler. Yes, the heat transfer is directly proportional to both the surface are and coolant flow, i.e. increase one or the other or both and heat transfer rate increases. Changing the flow rate clearly does not change the surface area or either the engine or the radiator. What increasing flow rate does do is decrease the thickness of the boundary layer. The boundary layer is an insulating blanket of non-moving fluid, so the thinner the boundary layer, the higher the heat transfer rate. No. Increasing the flow rate will always improve the heat transfer. The turning point of the systems ability to cool better is when the heat generated by friction of the moving fluid and the by pump inefficiency is higher than the gains due to improved heat transfer. From a system optimization standpoint, running the pump slower uses low power, so that is good. But that causes a higher temperature rise in the engine along the fluid path, i.e. the water goes in at say 150F and comes out at say 190F, so parts of the engine near the outlet are not cooled as well as parts near the inlet. So you determine the maximum allowable temperature rise or differential and set the pump speed to achieve it. Then the radiator size can be chosen to reject adequate heat at the given flow rate to maintain the system temperature within limits.
And this is where your theory blows up. If the fluid has less time to gain heat from the engine ... guess what?, it is not taking the heat away from the engine and thus cooling it as well!! Pumping the water too fast does not work for reason stated above, plus there are linear flow issues as well, which just make it worse. With any heat transfer between too materials there is an ideal flow rate for maximum heat transfer from the hot to the cooler ... fnck with that and your efficiency drops. This is exactly the same as any other heat transfer issue ... and you need a thermodynamics engineer's advice, not some car engine pump salesman. Pete
Theory is nice, but lets deal in the real world. The stock water pump doesnt not pump too much coolant. In fact, cavatition becomes an issue above 4,000 rmp, which reduces the amount of GMP pumped. The stock radiator core creates additional resistance to flow because of the relatively small coolant tubes. This problem is exacerbated by corrosion that renders the tubes internal diameter even smaller. Engines can run much hotter than the stated temp on the thermostat or the operating temperature referenced on the temp gauge. To a point, a hotter engine produces more power. The limiting factor is hot spots in localized areas. In the 4-liter engine coolant is a critical issue because we have encroached into the water jacket to increase displacement. The solution is to increase the efficiency of the water pump and radiator. At the risk of being redundant, the water pump requires less horsepower to turn the same rmps and doesnt cavatitate like the stock pump. The aluminum radiator can transfer approximately 50 percent more heat energy from the coolant. For us this is a good starting point, but the thing that makes the whole deal work is Evans Coolant. Evans NPG + has a boiling point of about 369 degrees F. As for the issue of how much flow is too much flow. Look at the numbers that I have previously posted. The stock Corvette pump generates 56 GMP and Evans high performance pump produces 85 GMP. 85 GMP is not too much for that application or they would not sell it. One the benefits of the Evans Corvette pump is that it pumps far more evenly to both cylinder banks. Now, the Corvette pump is a much larger unit than our upgraded 308 pump. The 308 pump still has to move coolant from the rear of the car to the front and back again. This is an extra load and our pump doesnt flow as much as the Corvette. So why are we worried about pumping too much coolant? We arent pumping enough coolant with a stock pump. Sincerely, Mark Lewis
No. As flow increase, each unit of coolant does pick up less heat, but there are more total units, so the net effect is more heat is carried out. No. In general, the more turbulent the flow, the better the heat transfer because the boundry layer is greatly reduced. In engineering, the term "idea" implies no friction, 100% efficient pump, ect. and is used as a simplification and often a first cut of the problem. There is no idea flow rate, it's all about compromise. Yeah, but I am a thermodynamics engineer (it's a subset of mechanical, I minorred in it)......and what Mark is saying sounds right to me. I think with a stock engine, the stock pump works fine, even if the seals aren't the best. The stock pump also seems to be ok in my engine, although I would consider the pump upgrade for the improved impeller. With Evans coolant, the new pump is probably a really good idea because the stuff is thicker and doesn't pump as well.
Okay ... good explanation. I actually took a thermodynamics paper many years ago ... guess I have forgotten plenty It does not sound right that you are giving less time to the water to take on heat, but I do understand that you are supplying more water ... and I have heard of plenty of people (my own engine was an example) that have slowed the water pump DOWN as the standard flow rate is designed to keep a car cool in traffic and thus over flows at race RPM. Anyway ... I'll pull me head in Pete
This from a racing board on water flow rates Can you explain how flow rates affect the cooling system? A combustion engine is basically a heat pump. Heat is the forerunner of power. You need heat to make power, and you have to be able to control how much heat is contained in the combustion space. If you dont, component damage can occur. The cooling system is basically there to absorb heat. Because of the passages in the cooling path throughout the engine, you are dealing with areas where flow tends to stagnate. Part of this is the physical passages available for water to move through. Another part, which is very important, is the fact that the temperature in the coolant is not uniform throughout the entire cooling system. You have hot spots, cooler spots and steam pockets. These variations in temperature cause the movement of the coolant to be different in different locations. The control of the temperature variations or extremes within the system is important. You would like for the range of that temperature to be as narrow as possible. As you narrow it, you begin to move away from the problems that steam pockets and hot spots cause. Problems may include excessive cylinder bore distortion, which can lead to cylinder head warpage and cause inefficient ring seal. The rate at which the temperature will move through a substance, whether metal or coolant, depends on the temperature difference. The more extreme, the faster it moves. What you are trying to do is stabilize dimensions in and around the combustion space. If it is too cool outside the combustion spaceif the water is moving so fast that it is too coolheat will be liberated from the combustion space into that coolant because the temperature grade is too extreme. You raise the temperature of the coolant and it begins to reject some of the heat loss. You would like for the coolant to maintain a reasonably high level of temperature so you dont lose a lot of heat out of the combustion space to a cooler environment. But you dont want that temperature environment outside the combustion space and the cooling system to have extremes in temperature. So, the rate at which you move coolant through the system will affect the temperature that is contained around the combustion space. When you have extremes in that coolant, you run into problems of periodic heat rejection and/or absorption in the coolant that is irregular and affects how much heat you are retaining in the combustion space. The whole idea is that you want to be able to hold as much temperature in the combustion space as possible because heat is power. But, you dont want it to be excessive. Excessive temperatures can lead to detonation, pre-ignition, lost power and serious problems in terms of part damage. The compromise comes in providing an environment for the combustion space that is not excessive. You would like it at 180 degrees F there and 210 degrees F here. To do that, maintain the proper kind of flow and introduce water or coolant in areas where there is not much flow by nature of the block design or head design. That is why extra lines are run because areas have been identified, and coolant is put into those areas to help reduce the temperature extremes due to lack of movement. If you move water too fast, it will be too cool and will lose heat from the combustion space. If you move it too slowly, you may have too high a temperature and develop steam pockets that restrict the flow path. The middle ground is to get the flow rate sufficiently high enough so it doesnt absorb too much heat from the combustion space. There is a see-saw effect here where you are balancing the temperature of the combustion space with the temperature in the cooling system so it doesnt lose too much heat if it is too cool, and it doesnt reject too much if it is too hot.
Yes, everything they say is correct (although incomplete) and in agreement with what I posted. What they are saying is higher flow rates cool more, what I am saying is higher flow rates increase the cooling capacity of the system, which is a subtile difference. They spent a lot of time talking about trying to achieve even temperature in the engine, but that is best achieved in most cases with higher flow rates. Cooling systems contain a thermostat and it is important beacause it allows the system to aviod to problem of the cooling water being too cold since only enough cold water comes in to keep the system temperature constant. As engine load and therefore heat generation rate go up, the thermostat opens and allows more water into the engine. But at the same time, because more water is going to the engine, more water is going to radiator and the temperature in the radiator begins to rise, until the cooling system reaches it's full capacity full at which point the engine teperature will begin to rise above the design limits. It's pretty simple when you get down to it. For example, on a hot day you are sitting in front of a fan set to medium. If you want to be cooler, do you turn the fan to low or the air has more time to cool you or high or you get more air?...slightly different principles at work, but the same concept.
From the engine side yes, but the radiator only can transfer so much heat to the air flowing thru it. Just like you stated, this will increase with air flow, but as I stated, at some point above or below this flow your ability to reject heat decreases. For a car, it's not so much a constant b/c the engine speed changes and the air speed over the radiator changes. But if we assume the heat rejection capabilities of the radiator are fixed, increasing the flow rate INCREASES the outlet temp. of the water at the radiator. Q=mCp(Ti-To) Q=Heat transfer m=mass flow rate Cp=heat coeff. (ugg, can't remember the exact name-has to do with the fluids properties). Ti=temp in To=temp out. Qair=Qwater If we say Qair is fixed (say sitting still with fans running), if you increase the mass flow rate of the water, T(out) of the water will go UP. If T(out) of the water goes up, and we now go back to the engine, the water still absorbs the heat at the same rate as before (as you said) so now To of the water out of the engine is hotter than before (To of water at engine = Ti of water at radiator). Now the water at the radiator is hotter and it's ability to reject he is fixed and the car overheats. Start moving and your car runs cooler again. So to make a blanket statement that increasing flow will increase heat rejection is not correct. It all depends on the system and application of that system, and the ability of the radiator to absorb the heat from the water.
Close, but no. Even if the system is air flow limited, it will still run cooler with increased water flow for several reasons. The surface of the radiator will be at a more uniform temperature. That makes the air that is flowing past the radiator more effective because more of it sees a hotter temperature. The water will transfer heat to the radiator better due to the reduced boundary layer, increasing the surface temperature of the radiator and making it more effective. So the net outcome will be that increasing the water flow rate produces a more uniform temperature within the engine and increase the cooling systems ability to reject heat under all airflow conditions. You can have a water flow rate that is higher than required and therefore wastes pump power, but you can not cause the system to run hotter by increasing water flow rate. The only real except is in the extreme case where the pump and flow friction are significant as heat generation terms. There is another case I can think of where temperature is being measured at a poor location, causing it to appear as though system temperature increases with flow rate (Ive seen that happen), but that is a measurement error and not real data. Remember too that its the system average water temperature that matters, not a change in temperature at any particular point.
I'm sorry but I disagree. The math says you are wrong. Q for one side has to equal Q for the other. While increasing the flow may reject more heat initially, AT SOME POINT, YOU WILL GO OVER THE SYSTEM'S ABILITY TO REJECT THE HEAT AND OVERHEAT THE CAR! If increasing flow was the answer, then why are industrial plate and frame heat exchangers different sizes? Why would a utility plant bother with changing the size of their heat exchangers if all they had to do was turn up the VFD on their hot water pump? BECAUSE THE HEAT EXCHANGER HAS A LIMITIED ABILITY TO REJECT HEAT! Why does Nick bother selling a bigger radiator for our 308's. All we really nead is a bigger pulley on the pump to increase flow. Wow, look how much money you just saved us! All smart ass talk aside, I do actually understand what you are talking about, but I disagree that increasing flow is the answer to overheating problems in the 308. Wait.. you're a pump salesmen aren't you!
Quote "If increasing flow was the answer, then why are industrial plate and frame heat exchangers different sizes? Why would a utility plant bother with changing the size of their heat exchangers if all they had to do was turn up the VFD on their hot water pump? BECAUSE THE HEAT EXCHANGER HAS A LIMITIED ABILITY TO REJECT HEAT! Heat rejection for a heat exchanger is not a constant. Increasing the flow of coolant through the radiator will cause the rejection of more heat from the engine and therby reduce the temperature of the coolant and engine. The tradeoff is the increased pressure drop through the radiator. In order to overcome the additional pressure drop - additional power is required of the water pump, and that decreases the available horsepower to the crank. We have to do an "energy balance," not just a "heat balance." The reason that power plants use larger heat exchangers when increasing capacity instead of turning up the VFD is that it costs alot energy to overrun the VFD and it is more efficient to replace the heat exchanger.
Qw=mCp(Ti-To) Qw=Heat rejection of the water Qa= heat rejection to the air (radiator to air). Qa in my example is constant. I understand that it will change as the air over it changes with the cars speed, but lets assume the car is sitting still in the driveway and the fans can only blow so much air over the car. The ability of that heat exchanger (the radiator) to remove heat from the water is fixed by the amount of air you push over it and the temperature of that air. While the 308 may be able to handle more flow, it is not infinite, even if you ignore the friction losses. In order to reject the heat from the engine thru the radiator (assuming no losses) Qa=Qw If the flow goes up what happens to the Ti-To in the heat rejection equation? Money for a new heat exchanger is never instantaneous. It takes weeks to get the $$ then months to get the new heat exchanger. Why can't I run up the pump in the short term? I can't b/c the temp. difference will drop. It's the same with a hot water boiler (a fancy heat exchanger). I can't simply increase the pump flow and expect more 190-deg water when it's already at capacity.
If the heat transfer from the coolant to the radiator is increased due to increased mass flow, Q is increased. As you say, the Q rejected to the air must be equal. This is done by increasing the temperature of the air exiting the radiator, increasing the delta T of the air. Qair = m(dota) Cp(air) [T(airout) - T(airin)] Qrad = m(dotc) Cp(cool) [T(coolin)-T(coolout)] I will admit that there is a diminishing capacity of the ability of the radiator to reject heat, and in this case is partially offset by the increased power necessary to circulate the coolant. I am not argueing that a new radiator (larger capacity) would not be a better choice, I just wanted to set the physics straight.
Yes, at steady state. What I am saying is that as flow goes up, the transfer coeffient goes up...heat moves into the water from the engine and moves out of the water into the radiator at a slightly lower temperature. Same Q, but created at a lower T. ABSOLUTELY! The main thing a bigger pump does is minimize localized hot spots, but it does also allow more heat to be rejected to the same amount of air because the impoved heat transfer of the water to the radiator increase the temperature of the radiator and the higher flow causes more of the radiators surface to be at the new higher temperature. Increasing the radiator size is the first and best step and I did say that earlier. As far as over driving the stock pump, simply increasing the rpm of a pump does not alway increase flow. The data Mark L posted say that it is already being driven faster than maybe it should be. The maximum flow is limited by head pressure (flow is inversely proportional to pressure) or in the case of the stock pump, cavitation sets in, at which point flow normally begins to drop with increasing rpm. It sounds like a misunderstanding here. I never ever said increasing flow will solve the stock systems overheating problems. All I said is that increasing the flow rate can only help and certainly will not CAUSE an overheating condition. 308s overheat because the radiator is barely adequate and must be maintained in near perfect condition. The answer is a larger radiator, that is what I did to my car and all the problems are gone....but I would consider also adding a better pump for good measure and I'm not concerned that it will make the car overheat at idle or any other rpm.
Mark, Nick. I received the new water pump today and I've got to tell you that quality of the casting and the impeller design is amazing. It mated up perfectly to the rear housing. I will be dropping engine back in next week and that have some work to do before starting it up. I will post when that happens. My 6 gallons Evans NPG+ should arrive any day. Paul
Hi Sam, the selling price on the pump at this time is $695.00, which includes the lightweight anodized pulley with pulley bolts & pump gasket. We have just set up a distributor in the UK for these pumps & we are looking for more distributors worldwide, for more info contact me at [email protected] Or via tel at 360 410 1949 Image Unavailable, Please Login
Nick, Seems reasonable. What does a water pump rebuild usually run ($)? BTW, the Electromotive I purchased from you 3 years ago has not missed a beat. Philip
Hi Philip, re builds seem to range around the country from $300.00-$500.00 parts & labor. This new pump as you have probably read in the earlier pages of this thread is completely re designed. All of (in our opinion) design flaws have been addressed. Glad to hear your Electromotive ignition is still working great. I am very happy with my Electromotive ignition systems in my Ferraris also. Here are a few pics, one also shows the difference in the inside components compared to OEM & the new impeller design (that is actually clear anodized aluminum) also another shot of a completed water pump. Image Unavailable, Please Login Image Unavailable, Please Login
I thought that I would share some of the conversation that I had with Steve Pressley of Evans Cooling. It seems that most of the chat sites for various performance cars eventually have a very detailed discussion about cooling and Evans Coolant. The last week or so on this thread has been focused on the cooling system upgrades for the 4-liter engine. There has been some concern regarding whether or not the new water pump would pump too much coolant. Please be advised that the engineers that have been consulted for the 4-liter water pump dont think so. In fact, we have been advised that it may be beneficial to overdrive the pump. The pumps that are being sold now have a stock size pulley, but the 4-liter engine will overdrive the water pump by about 20 percent. The reason that the new pump is not being sold with an overdrive pulley is simply a matter of ease of installation. You dont have to replace the belt. If people want an overdrive pulley, we can get you one. Many OEM water pumps are actually under driven to avoid cavitation. As previously mentioned, we have estimated that cavitation for the stock 308 pump sets in about 4,000 rpms. If you have a scroll type impeller then the onset of cavitation is delayed, but flow will max out between 4,500 and 5,000 rpms. Cavitation really messes up both coolant flow and cooling efficiency. Evans Corvette water pump produces about 85 GPM and ultra high performance versions are over 100 GPM. This is not excessive when combined with a radiator of similar design to our new aluminum one. Even though we are probably doubling the flow capacity of the stock water pump, we are not close to the numbers for the Chevy pump. Sorry guys, if you are suffering from pump envy, then buy a domestic high performance pump. The 308 housing is small. The 308 impeller is small small as in Ford Pinto small. We have substantially increased the flow capacity, but we should not deceive ourselves into thinking that this is a huge pump. We have made a small pump a far better small pump. Some have worried that we are pumping coolant too fast through the radiator to efficiently dissipate heat. This is not the case. The smaller copper tubes in the stock radiator resist flow and actually increases the velocity of coolant through the radiator. In fact, the boundary layer of coolant in these small tubes moves very slowly while the coolant in the center of the tubes flows very quickly. This impedes heat transfer in the radiator. In the aluminum radiator there is about 40 percent more tube surface area. The tubes are oval in shape and are 1.25 inches long. This increased tube size results in increased flow and turbulence. The additional turbulence actually dislodges the boundary layer and aids in heat transfer through the radiator. For those worried about too much flow, it is important to remember that the water jackets in the engine effectively reduce flow by about a third. The radiator will restrict flow even further. What we have done is both increase pumping volume and reduced restrictions within the radiator. How much heat energy can the new radiator handle? A double row, 1.00-inch tube, aluminum radiator can handle between 400 to 500 hp. Our aluminum radiator has 1.25-inch tubes and is rated at over 500 hp. This explains why those that have switched to an aluminum radiator have noticed lower coolant temperatures. The aluminum radiator can transfer more heat, but this is only part of the picture. The increased turbulence generated by the new water pump reduces hot spots in the engine. The lower flow and predisposition towards cavitation of the stock pump actually invites hot spots. This is why the 4-liter engine will use both the upgraded water pump and the new aluminum radiator. I guess I will save most of rest of my conversation for my next post. Sincerely, Mark Lewis
