Landracing Forum
Tech Information => Technical Discussion => Topic started by: Jonny Hotnuts on March 17, 2007, 02:54:18 PM
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OK, here?s the deal.
I am putting together a busa powered LS car to compete in Mod-Sports class.
I have installed a Meziere electric water pump (needed the room for chain routing to the drive and the stock pump was in the way).
http://store.summitracing.com/partdetail.asp?autofilter=1&part=MEZ%2DWP136S&N=700+400027+115&autoview=sku
I have been getting conflicting info from very credible sources regarding the use of an electric pump.
The conflicting statements are as follows:
?If you use an electric water pump you must pre-pressurize your system as an electric water pump can not develop the necessary pressure to prevent water from boiling in your head. Water pressure is made behind the radiator and thermostat and while an electric pump can flow like a garden hose the fact is that for every pound of pressure you loose 2 degrees from boiling. The system needs about 15 pounds (will equal -30 degrees from boiling so your boiling temp will change from around 212 @ sea level to 242) and an electric pump can only make about 4. At 4 pounds the boiling temp will be about 220 and you will get boiling in the head and?.detonation.?
(Seems very plausible, and not a big deal to install a fitting in the radiator that I can pre pressurize the system with about 15 pounds of pressurized water (to avoid air in the system).
BUT I ALSO WAS TOLD:
?Once the temp of the motor starts to raise the heated water in your system will generate the pressure, and it is not because of the flow restrictions of the thermostat nor the radiator (argued that a system without a thermostat will make pressure anyway), so adding a way to pre pressurize the system is not needed.?
So who is correct?
Thanks
Jonny
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I'm no expert but I firmly believe that #2 was the right answer. As the water heats and expands pressure is built. Some restriction to the flow may be a good idea as in having a thermostat at the outlet, to insure the water is flowing everywhere is should. Dave may jump in here with the scientific answer.
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A pump is used to move water. Water is not compressible in this system. If you have an open system, like from one bucket to another, the pump can't achieve pressure because the system is open. If you restrict the system with a smaller opening, you can bring the pressure up, but the flow drops also. If you restrict the intake, the pump output will be less, and at some point will starve the pump and it will cavitate.
But this isn't an open system, it's a closed system. Everything that goes out the pump comes back through it. Unless there is a restriction in the system the pump can't achieve pressure, electric or engine driven. But there are restrictions.
To think of the cooling system as just a pressurized container for coolant is misleading. In a simple container, pressure is equal in all directions. Cooling system pressure, however, is average pressure, usually measured at the radiator return tank. Actual pressures vary throughout the system. Coolant circulation is vital to heat transfer and temperature control.
Pressures are highest at the water pump outlet and in the water jackets near the combustion chambers. System pressure is lowest at the water pump inlet. Pressure is generated by the water pump and controlled by variable restrictions, like the thermostat and valves in the radiator cap. The system also has fixed restrictions, such as orifices in the water jackets and passages in the radiator.
If you just sealed the system and ran it, the system would continue to create pressure until something let go. Using a radiator cap that bleeds pressure off at a certain pressure keeps that from happening.
The real pressure in the system comes from the heat of the engine. The system is pressurized to raise the boiling point of the water above 212 F. Raise the pressure to 15 psi and the boiling point goes up to 250 F. Add radiator coolant, like ethylene glycol and 15 psi gets you 265 F.
As the engine creates heat, the water flow and pressure have to remove enough heat to avoid steam. Steam will allow the spot temperature at that point to skyrocket. Air in the system will allow steam pockets even if everything else works just fine. The highest point in the system is where air will go, and you have to have a bleed there. High spots in the circulation path will also collect air. Avoid them if possible, if not, realize that you are going to run with some air in the system.
I can't see where pre-pressurizing will gain you anything. The system pressure is zero when you fire it up. The heat load is low because you aren't generating much heat at idle. The water pressure is coming up, but even at a low pressure, there isn't much heat because you have to get the engine up to temperature. As you accelerate in 1st gear or at some point in the curve, the engine will be near to as hot is it's going to get. During that temperature rise, the pressure in the system is rising along with it.
I don't see anything wrong with pre-pressurizing either. You start with a system that has a 265 F boiling point. But I don't see that it would make a difference if it is an electric pump or engine driven. Only if the electric pump is under the flow capacity of the engine at some point, and I wouldn't run something like that.
The amount of flow has to match the ability of the radiator to remove heat. All the flow in the world won't help if the radiator won't handle the load.
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Read the Mod.Sports rules very carefully, there are restrictions on the class. What type of production body etc. How many were made of that vehicle body. It's a little tricky.
Glen
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Wow, thanks for the answers they have definitely made this come to light.
Glen, I am surprised that you would say that, the modified sports class (as with all the mod classes) is IMO one of the most liberal classes to compete in openly allowing things that I, even as a car builder, think are pushing what the class should be.
It is however an important thing to say to someone given that I am new to this forum and unknown here but I am not unknown to the salt and have been at regular attendance for a "few" years now.
This is MY first car and I am working in conjunction with the advice of Jim Miller who as been very helpful in clearing up the "Grey" areas that is the blood of the SCTA-BNI rule book. I do appreciate the concern, and hopefully tech wont be too hard on me (wishfull thinking!).
Here is a pic of me:
(http://www.fiatforum.com/gallery/data/500/medium/Picture_0631.jpg)
And a few pics of the car in progress (not current photos but an idea).
(http://www.fiatforum.com/gallery/data/500/medium/multi.jpg)
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Jonny
Not trying to discourage you. You didn't say any thing up front on what you were planning to run. It looks like a neat little project car and light enough to have some fun with. One thing is I hate to see anyone get caught short when building a new vehicle. It's generally a long way to tow. Jim Miller is a good source to go to. Oh, BTW, welcome to the forum, it's a great place to land and make new friends. What area do you live in, is some cases there are others that can help if you are somewhat close. Keep sending pictures they help.
Glen
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Glen, I did not take that as something discouraging.
I think its important to let someone know what is expected in building a car and even with a fairly good knowledge of the current rules the fact remains that the rules change or can be interpreted differently and it is a long way.....not to mention the hotels, fees etc.
I am concerned about the weight, but thankfully the motor is over the drive wheels. I will do some testing on a dry lake before august but I think I have the COP far enough back that it will drive straight. I dont want to add ballast if I can solve it with a nose!
Portland Oregon.
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There are a lot of LSR people in Portland including Marlo Triet, we just last month had the NWLSR banquet, to bad you didn't know about it. It is at the Airport Shilo Inn every February . Hooking up with any of the racers would be a good thing.
Glen
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OK, here?s the deal.
I am putting together a busa powered LS car to compete in Mod-Sports class.
I have installed a Meziere electric water pump (needed the room for chain routing to the drive and the stock pump was in the way).
http://store.summitracing.com/partdetail.asp?autofilter=1&part=MEZ%2DWP136S&N=700+400027+115&autoview=sku
I have been getting conflicting info from very credible sources regarding the use of an electric pump.
The conflicting statements are as follows:
?If you use an electric water pump you must pre-pressurize your system as an electric water pump can not develop the necessary pressure to prevent water from boiling in your head. Water pressure is made behind the radiator and thermostat and while an electric pump can flow like a garden hose the fact is that for every pound of pressure you loose 2 degrees from boiling. The system needs about 15 pounds (will equal -30 degrees from boiling so your boiling temp will change from around 212 @ sea level to 242) and an electric pump can only make about 4. At 4 pounds the boiling temp will be about 220 and you will get boiling in the head and?.detonation.?
(Seems very plausible, and not a big deal to install a fitting in the radiator that I can pre pressurize the system with about 15 pounds of pressurized water (to avoid air in the system).
BUT I ALSO WAS TOLD:
?Once the temp of the motor starts to raise the heated water in your system will generate the pressure, and it is not because of the flow restrictions of the thermostat nor the radiator (argued that a system without a thermostat will make pressure anyway), so adding a way to pre pressurize the system is not needed.?
So who is correct?
Thanks
Jonny
Maybe I missed it, or you going to run a water tank or a radiator??
Also how about some larger pictures??
Sum
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hey hotnuts
how big is your water tank? I have a 30 gal water tank in my liner for ballast and a meziere pump that feeds both zx1100 motors. I preheat my water to 180 then turn the pump on and warm my blocks up before i fire my motors. i can run the loing course and still be under 230 in the tank. my system is sealed and i do not pre-pressurize my systern at all. dont worry about it, it will work great, my suggestion would be to run about a 20 gal tank in the nose of the car for ballast and put a restrictor in line so you dont over flush your system... that meziere punp will move so much water that it wont let the water soak up and disipate the heat..... slow the flow down a little and go have some fun.
kent
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All the above aside Jonny xxxx will have to have some type of radiator in Mod Sports.
DW
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Dwarner is correct, I am running the stock busa radiator but use 2 fans (stock uses 1).
1212FBGS: noted and will take under advisement.
Sumner, when I try to post the pic larger it somehow defaults to the smaller size....
here is the pic as it should be but its not posting:
http://hayabusa.org/iB_html/uploads/post-12-39123-multi.jpg
Glen, I did know about the NWLSR banquet but was unable to attend because of the nut-farm I call work.
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Interesting that we have another "water pump" thread, I was going to start one myself but this is a good one to add my thinking.
I was reading the latest "Racercar Engineering" and they had a very good article on the Cosworth F1 V8 engine in which they gave some interesting numbers regarding it's cooling system. The engine AND the radiator only hold 4 liters of water! total! and the pump volume is 270 liters/minute!!! So Dan Warner's comment regarding slowing down the flow may not be what you should do. With extremely high rates of flow the water is very turbulent which means that each molecule of water is brought into contact with the hot parts of the engine and also with the cooling tubes of the radiator many times which allows for greater heat dissipation, also the very high flow rate through the engine helps eliminate any hot spots as they are literally sweep away by the high velocity water. This information also backs up the rule for water pump flow that Stu Van Dyne has always gone by, 10 gpm/100 hps.
Your car looks like it should be fun, going to make this year?
Rex
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I don't recall my input as to water flow.
I do know that we have not used an electric water pump since the late 90s. Ed Pink told us that you MUST fill all possible heat pockets. We have used a JFK sprint car pump for the last few cars. Works swell.
We heeded Ed Pinks advice - it was free, how much would your attorney have charged for those minutes?
Results? An El Mirage Championship, a Bonneville record over 250 in only three miles, what else do you need to know?
DW
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I could never understand why anyone would want to preheat water used for engine cooling or run without a thermostat if they had the ability to start it and warm it prior to a run. The whole purpose of the water is to absorb Btu?s and remove heat from the engine. Heating it just reduces the amount of Btu?s that can be absorbed by the water. The thermostat in modern engines does exactly what it is designed to do, regulate temperature of the engine within the limits for which it was designed. If you start and run the engine for a short time prior to a run and then let it heat soak while you are waiting to run at high power it will be at the proper temperature by the time you are 1/4 mile down the track. The same thing goes for oil also unless you are running straight 50W and it is 10 degrees outside. Oil absorbs Btu?s when it heats that?s why they make oil coolers. Modern multi weight oils lubricate just fine at low temperatures.
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Ack gets up earlier than most and that gets him thinking sooner with more predictable results.
This may come as a shock but even oil systems cam be fitted with a thermostat that will bypass the cooler.
Oh, and he is right in this one too. :wink:
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Your car looks like it should be fun, going to make this year?
Rex
Rooms and dues paid....... ;)
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Sumner, when I try to post the pic larger it somehow defaults to the smaller size....
here is the pic as it should be but its not posting:
http://hayabusa.org/iB_html/uploads/post-12-39123-multi.jpg
I separated the pictures. I'll be interested in how you do as I'll probably have a busa someday in my lakester. My only comment would be make the spill plates a large as the rules permit. It looks as if they are as high as permissible, but keep that height as far forward up to the axle center line as possible to get every benefit you can from them in regards to the "center of pressure".
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.........and the last one,
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I pre heat my motors to warm and expand the blocks before I start them! Yeh cold water makes more horsepower bla bla bla! On a dyno. I tell ya a warm motor will love ya even more?and it will stay together. We use to make those cold water passes and pretty much hurt a motor every pass!!! At 30+lbs of boost it don?t take much to squeeze a head gasket out. Started pre heating the motors and haven?t had a problem since. Go to the drag races? watch those turbo boys slowly warming there motors up? they know the combustion temp wont warm the blocks up fast or evenly enough to keep a head gasket in it. Thermostats are for street motors ever had one stick shut? Just one more useless thing that can break and go bad.
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If a thermostat fails shut is is caused by overheating that made the internal expansion system lose it's ability to operate.
If the installer doesn't understand it's operation it might be installed backwards with a similar result.
The proper , unloaded warm up procedure with a thermostat includes watching the temp rise very carefully and when it starts to dip that tells you it is open at the specified temperature and you are now starting to preheat the rest of the system.
A proper thermostat system will keep the engine at the desired temperature with everything else just an Old Spanish Custom.
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:roll: Jack, you are up today before Ack, good job.
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:roll: Jack, you are up today before Ack, good job.
As these kids get smarter and smarter, ya gotta get up earlier and earlier. LOL
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I may not be the sharpest tool in the shed but I can see logic in preheating water and I by no means suggest that what I am going to suggest is correct?.but?.
I can agree that the conventional logic of having your mechanical thermostat regulate the temp of the water is a good one and therefore preheating your water would not be the best thing to do. This logic has been tried and true since the inception of the automobile and why change it?
For whatever it is worth I can see how the use of an electric water pump WOULD justify pre heating the water. Preheated water would prevent the electric pump from running on a full restricted load by the thermostat. In my limited experience with electric pumps I find it is hard on a pump to block its flow 100%?.. I feel that over time that running an electric pump under full restriction will eventually cause premature failure where as a crank driven pump does not care.
Something that would be interesting to try by someone using an electric water pump would be to remove the thermostat (this would increase the flow capacity and cooling ability) and install a variable temp switch in the water jacket. The variable temp switch would regulate the operation of the water pump as appose to a thermostat regulating flow, the flow would be regulated electrically. Not only would the cooling system be more efficient, it would be easier on the electric water pump but you could also on the fly regulate the temp of the motor by turning a knob. This could also eliminate the hands on procedure of turning the pump on or off?.it would do in automatically and be one less thing to do.
Longevity of the water pump may be a minor reason to preheat the water?.and regulating the water temp electrically as apposed to a traditional thermostat may be a waste of time with no real practical benefits??but that is no reason that someone using an electric pump should not do this??just not me?..but let me know how it works for ya!
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and thanks Sum for fixing the pics.
-JH
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To much foo foo presents too many problems.
An electrical anything will be less reliable that a mechanical thermostat.
If you wish to not dead head any electrical pump system a very reliable thermostatic switch will keep it off until you need it.
If you don't trust that , the old toggle switch you already had can bypass even that.
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the more trickery you design into it the more stuff to fail especially electrical stuff on the salt. as far as remembering to flip a toggle switch at one point of a pass....your better off doing your pre race prepwork before you jump into your car.
good luck
kent
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I agree with Jack about too much "foo foo". However I think keeping the water circulating through the engine [closed loop] until it comes to temperature will keep hot spots to a minimum and warm the engine uniformly. When using a remote water pump this can be accomplished by using electric solenoid valves,opening and closing the bypass. Use either thermostatic or manual [toggle switch] control. just a thought, Don
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If the cooling fluid is working at all the Hot spots will be averaged during a proper warm up and harmless.
If the design for flow is bad under load that is just bad no matter how you circulate the juice.
If your ability to monitor water temperature is limited when you are underway than I have nothing to offer.
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Just a quick comment regarding running your electric water pump with the outlet closed, as these are centrifugal pumps when you close off the outlet the pump goes into stall and the actual power to run it drops!
Rex
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I was not implying that idea was something I was going to do; rather to the contrary, to me it was just an idea.....but....
A few made the suggestions that one could use a thermostatic control switch to prevent the pump from "dead heading".
That is exactly what I was saying to begin with..... with the exception that if you used a thermostatic switch you should NOT also need the mechanical thermostat in the motor. I suggested that you could use a variable thermostatic switch, and this would allow you to change the operating temp of the motor. If you used a set value thermostatic switch to run the pump, it would be the same as having a mechanical thermostat of that same temperature.
I would like to know if the BS that I am suggesting is correct......if you use a thermostatic switch to run the pump you do not need a mechanical thermostat in the motor.
-JH
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The mechanical thermostat that you depend on every day that will out last the family car is cheaper, more available , and reliable than just about anything you can put on a racer.
If your system demands an electric pump you can duplicate the symptom of a dead head by covering the outlet of your shop vacuum and listen to the motor unload as does the current required to drive it.
These are basics that you already know, are a good place to start, and it helps you to finish with all your stuff intact also.
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It many not make any difference but you can check out this site for electric pumps. www.batinc.net Go to the Mocal systems. The have an electronic controller for their 12 volt water pump. I have never used anything but a restrictor in the return line to control the coolant water but I don't make the heat or HP of many. My only concern with a lot of the pumps is how munch pressure the seal will withstand. Good Luck...Great Thread
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One thing we found on some electric pumps they will stop if the water gets too hot. Not a good thing, so watch out for the plastic impellers in the "water puppy" type pump, only good for 212 or so on the water temp.