GM LFX V6

Discussion in 'General Auto Conversion Discussion' started by pfarber, Apr 26, 2019.

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  1. May 17, 2019 #121

    rv7charlie

    rv7charlie

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    I used to lean toward a similar assumption, until someone with an actual engineering degree explained why it isn't true. According to engineers, the thing that matters is temperature delta. If the water stays in the rad longer, then yes, it will cool down more. But (a big but), once the water temp starts dropping, the heat exchange efficiency starts dropping rapidly. Lets say you get the 80* drop someone mentioned. If the water starts at 200* and outside air temp is 100*, heat will flow great at the 100* delta. But what happens to the water that's down to say, 130*? Now you only have 30* delta, but you're flowing the same quantity of air through the heat exchanger. If it's cooling a 1500 lb diesel pump engine sitting beside a pond, that might be ok. But it's a massive quantity of wasted cooling drag in an a/c. And a 3 pass rad will have 3 times the flow resistance of a single pass, all else being equal. So it takes more power (at ~30% engine efficiency, 70% added heat) to pump the water against the extra resistance. Only exception I've seen that works is a 2 pass with the hotter flow behind the cooler flow, to keep temp delta as high as possible. And it's typically done to compensate for packaging issues (face area on the a/c), rather than to improve rad efficiency.

    edit: Another thing to ponder is: What will be the effect on engine longevity if water is exiting the block at ~200*, and re-entering the block at 120*?

    The guys I know who are cooling *efficiently* see a *much* lower water temp drop through the rad; <20* instead of ~80*. Once everything is optimized, there's very little block output to rad output temp drop, because the rad is keeping the temp very close to set point.

    The thing that I've never seen any good data on, is how much flow is needed for a given output, and how much energy is wasted when you pump too much water (obviously no single number; every situation would be different). Just a wild guess, but with mileage and emission laws being what they are, I'd be fairly confident that if the car mfgrs didn't see some efficiency improvement from being able to modulate water flow using an electric pump, they wouldn't be adding the complexity and the need to convert mechanical energy to electrical and then back to mechanical to run the pump. Having said that, I wonder if it makes sense in an a/c, unless there's a 'packaging' issue. ex: the old Mazda 13B engines had their water pump 'snouts' sticking up about 6" above the block; almost impossible to package in a typical cowl. Even then, a decent TIG welder could solve the problem of the stock pump.
     
    Last edited: May 17, 2019
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  2. May 17, 2019 #122

    poormansairforce

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    There it is! And the finger on a weld example doesn't work because we're missing the effect of turbulence. Slow water flow equals laminar flow. Not good for heat exchange.
     
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  3. May 17, 2019 #123

    rv6ejguy

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    Modern cars often use electric pumps which can be flow modulated by the ECU. Cars only need about 15-20hp to cruise at 60mph so you don't need much water flow to cool most of the time. There is probably .1-.2 mpg there so they feel that's worth it. Aircraft cruise at a much higher relative power setting so doubtful that's worth it. I wouldn't bother replacing the mechanically driven pump on my Sube. It all works just fine with 3/4 inch plumbing to the rad.

    I do have a customer using an electric WP in his aircraft. Working fine so far too.
     
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  4. May 17, 2019 #124

    poormansairforce

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    This has been my whole point to you. You just proved to yourself why this won't work.
    And then there is this gem from your resources:

    Following is a typical engine:

    Inlet temperature = 180 F
    Outlet temperature = 190 F
    Coolant flow = 100 GPM
    Specific heat of coolant = 1.0
    1 HP = 5.2769885 GPM 1 F
    { (Outlet-Inlet)CS} / 5.2769885 = HP loss
    {(190-180) 100*1.0} / 5.2769885 = 189.5 H

    And this one:

    The radiator becomes less efficient as the coolant outlet temperature approaches ambient. Therefore, a low flow rate keeps the coolant in the radiator longer. The longer the coolant stays in the radiator the lower the efficiency of the radiator.

    So no one has had to convince you why It won't work, you have already done that for us. I wish you the best of luck with your project.
     
    Last edited: May 18, 2019
  5. May 18, 2019 #125

    pictsidhe

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    Water to air heat exchangers tend to have one thing in common. The wet side has a far higher heat transffer coefficient than the air side. Water is much denser and has a higher conductivity. Speeding up the water flow will increase the heat transfer coefficient, by a miniscule amount once you factor in the comparitively dreadful heat transfer of the fins to air. the only thing to worry about on the water side is the volumetric flow rate. Single or multi pass makes little difference unless the air also makes several passes, or you have two cores, one behind the other. The amount of water that you need to pump is quite easy to ballpark IF you know the temperature delta that the rad will support, which depends almost entirely on it's ability to heat air, not cool the water. Once you have done that, tweak with alternative pulleys. I believe the rule of thumb is one cubic inch of modern car radiator per horsepower? I'd be inclined to experiment with cheap junkyard radiators before buying a new one once the size is nailed down.
    Most of the cooling system power loss is drag on the air side, so it may well be worth using a bigger, heavier radiator to reduce that. We are very lucky in that modern car radiators are very reliable, surprisingly light and good at dissipating heat. If we diffuse our cooling air efficiently, we can have a lightweight and low drag cooling system.
     
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  6. May 18, 2019 #126

    pfarber

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    Self deprecation, I called myself stupid and STILL someone gets it wrong.
     
  7. May 18, 2019 #127

    pfarber

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    What part of better cooling, less weight and more power generated by the engine is in dispute?

    You're killing a lot of electrons to debate the absolute minutia of scenarios that have no real impact.
     
  8. May 18, 2019 #128

    pfarber

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    Your post does not say what you think it does. Really.
     
  9. May 18, 2019 #129

    pfarber

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    http://www.contactmagazine.com/Hangar_Talk/August-08/John_Steere.html

    "When the shop completed the radiator, I found it to be much thinner than I had requested. Instead of the specified 2.5 inches thick, it was only 1.2 inches. Based on his experience with auto racing, the shop owner believed it would be sufficient. So I mounted it and flight-testing has proven that he was basically correct. However, there have been times on hot days, during long climb outs, that the thicker radiator may have been beneficial. "

    Dwell time in the radiator is a consideration, but as we all know, radiators lose efficiency as the coolant approached ambient temp. So you have to balance the flow rate and temp drop created by the radiator. In laymans terms you want to put coolant though the radiator just long enough to get the most cooling (20-40deg) then cycle it back to the block. This balance is controlled by the thermostat. It will flow coolant fast enough to maintain its set point. Once this balanced state is obtained, the water pumps max GPM, as long as its sufficient, is immaterial.

    But since, in an AC, we have to strike a balance between cruise performance (max cooling) and minimum cooling (taxi) and significantly reduced cooling at high power (climb out) the best answer (to me) is to have a pump that handles all three phases equally well. The BIGGEST advantages of the electric pump are:

    ALWAYS MAX GPM, lighter weight, less power used. Ok, say that the electric water pump costs 2-5hp more (they don't. Every Dyno has shown that the electric pump costs less HP than belt driven), at what point do you dismiss the OTHER TWO MAJOR ADVANTAGES????????????????

    We all agree cooling is the biggest headache, and hard to get right. So when a much better tool to cool the engine is found, people talk about minutia that has no real bearing on the three main advantages: high GPM, less weight, less power consumed.

    "A thorough study of available data on water-cooled aircraft engines was completed and data from the most successful installations was used for guidance. The data indicated the design targets for the active frontal area of the radiator should be one square inch per horsepower, and the radiator volume should be 2.52 cubic inches per horsepower. "

    With a goal of 250hp the rough math makes the cooling requirements fairly modest. An opening of 250sq and a radiator volume of 650cu/in. Not large at all.
     
  10. May 18, 2019 #130

    wsimpso1

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    This is what I have been talking about. For the rest of you, there are many things wrong with this:

    "Better cooling" - We have not seen anything that indicates any need for more cooling at any engine speed than we get with a conventional water pump running standard or modest underdrive pulleys, as has been done with quite a few automotive conversions. More flow than needed is not better, it is just wasted energy;

    "Less weight" - Data has not been presented on the all up weight of pump options. We all have good reason to think that any electric pump capable of moving sufficient coolant to keep the engine temps in bounds at continuous high power settings will require a larger alternator than would otherwise be needed, so weight could indeed be driven up not down;

    "More power generated by the engine" - The ingoing assumption in the one seriously flawed test presented is that the engine generates the same power while we find out what the accessories are subtracting by looking for changes in measured output. Never mind that we have no assurances that power stayed the same, nor any indication that the dyno is repeatable enough to actually measure the differences after the accessories draw some power...

    Then there is the little issue of: Power to run the electric pump comes from the alternator with bigger losses that way than from simply routing the belt to the pump; and the aftermarket pump runs one speed all of the time, thus increasing energy use when the alternator is running slow, possible discharging the battery until the flight is commenced, with the risk that entails. You might save some power over parts of the operating range by trimming back pump speed (and power) to that required as dictated by either mapping of throttle and engine speed or simply servo-ing the motor speed based upon top water temperature.

    What is in dispute? Dear readers, everything pfarber wrote above. And he can not prove it so he shouts.

    No electrons were killed or injured in the writing of this response. A modest number may have been momentarily inconvenienced but they are being pushed about all of the time that the servers and this computer are sitting here running, whether I write a note or not.

    Dear readers - pfarber can do what he wants with his airplane project. I want to see him build it and show us what he is doing and share his engine data on his test flights. If it works fine and performs great, terrific. But as long as the alternator is being spun and maintaining the battery in flight, he is unlikely to have more power at the prop over our typical flight dutycycles this way than with a belt that runs the pump at an appropriate speed during takeoff and climb power settings...

    Billski
     
    Last edited: May 18, 2019
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  11. May 18, 2019 #131

    poormansairforce

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    Then what does it say? Care to enlighten me?
     
  12. May 18, 2019 #132

    pictsidhe

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    Perhaps this would be a good point to thank pfarber for this most enlightening debate. It has made it abundantly clear how useful the information and products in hot rod magazines are.
     
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  13. May 18, 2019 #133

    Himat

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    A guess is that legislation have something to do with it too. One thing is a .1 to .2 mpg improvement, another is a .2 improvement or more at the fuel mileage test cycle. A car manufacturer may be able to program the ECU to run down the car battery as much as tolerable for the duration of the test. The results are then massaged to a better number.

    Several countries do tax cars by the fuel consumption and/or emission, everything that dodges the tax improve sales. Some customers may complain that the mpg numbers are not realistic, others understand the relationship between a lower car tax and in practice not attainable fuel consumption.
     
  14. May 19, 2019 #134

    wsimpso1

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    The rules are very specific that you can not run down the battery on the cycle on conventional vehicles. Electric coolant pumps are used to get better fuel numbers. Here is how:

    The EPA and Euro fuel economy/ emissions cycles start after a soak at modest temperature, and then they are run at modest speeds, accels, decels, stop sign and traffic light stops. The highway cycle is short and only goes to about 55 mph. The air conditioning is NOT turned on and the Defog/Demist setting is not used either, so the AC compressor is never engaged. These are all somewhat unrealistic, but that is the standard.

    Is this unrealistic? A little. But the Europeons and Japanese have very similar routes and drive cycles on their cert cycles too. The Euro cycle was supposedly decided upon after a lot of studies on customer driven cycles. I do know that it does not represent my cycle , but I live in the country, go 62 mph to go to the grocery and hardware store, run my AC and go 78 mph on the interstate.

    Until the engine is reaches planned top water temps, the electric coolant pump is either run slowly or not at all. Once top water temp reaches planned running temperature, the pump is run no faster than is needed to keep the coolant temp where it is supposed to be. Since the cycle runs the engine at only modest power and since many cars are also stop-start (not even idle power when stopped), a good chunk of the driving is at very modest coolant pump power, and the electric pump results in saving a measurable amount of fuel. At WOT, something that most road users run very little of, they could even cut out the alternator and AC compressor for a few seconds to boost acceleration. When those same vehicles are running continuously at 50-75% power like we do when we climb or cruise in our airplanes, I seriously doubt that the electric pump is saving any power at all and probably costing them some output due to losses at the alternator, wiring, power electronics, and electric motor.

    Billski
     
    Last edited: May 19, 2019
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  15. May 19, 2019 #135

    mm4440

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    Hi, cooling problems are almost always due to inadequate airflow through the heat exchanger. If the heat exchanger is big enough and the coolant flow is adequate to prevent hot spots and steam blanketing in the heads; all should be well. Electric drive will take about twice the amount of power from the engine to move the same amount of coolant. The belt drive which is needed to drive the bigger alternator anyway is much more efficient than the electric drive combination and costs and weighs less. I suggested using a heater core and blower that can provide cabin heat or supplemental cooling with an overboard hot air dump when cabin heat is not needed.
    An electric pump in series with a belt driven pump could be useful; a subject for another post.
    Non water based coolants are another subject for another post. https://www.evanscoolant.com/
     
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  16. May 19, 2019 #136

    pfarber

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    By your logic, a 200GPM pump would be better than a 100GPM pump. There are rules of thumb to size the cooling system that utilize stock pumps for AC that work well. You'd be hard pressed to find a stock production water pump pushing 100GPM. Half that is more correct. At idle? 1/10th of that.

    Cooling is a balance of airflow through the radiator, the surface area of the radiator, and the amount of water passing though the radiator.

    Considering two phases of flight that have historically causes cooling issues (taxi and climb out) are the the worse cases for the engine driven pump finding a suitable replacement is an important goal to accomplish.

    Tell you what. PROVE ME WRONG. I posted my findings and debating all of tangential minutia laden half thoughts is not getting my engine built.


    Now on the Billski... I'm really getting tired at beating this dead horse: Yes, I used caps. Evidently I need a big hammer for thick heads.

    ""Better cooling" - We have not seen anything that indicates any need for more cooling at any engine speed than we get with a conventional water pump running standard or modest underdrive pulleys, as has been done with quite a few automotive conversions. More flow than needed is not better, it is just wasted energy;"

    Did you not read my post about the SAME airframe I have (BD-4B) and a similar engine (V6) HAVING COOLING PROBLEMS DURING TAXI? I mean I POSTED AN INDEPENDENT ARTICLE ABOUT THE EXACT THING YOU SAY IS NOT A PROBLEM BEING A PROBLEM.

    ""Less weight" - Data has not been presented on the all up weight of pump options"

    My gawd.. some peoples kids. Did you not read the articles that stating, unequivocally, that the electric pump was lighter than the stock units?

    ""More power generated by the engine" - The ingoing assumption in the one seriously flawed test presented is that the engine generates the same power while we find out what the accessories are subtracting by looking for changes in measured output."

    Oh lordy... I mean after multiple articles, dyno tests and charts and tables, you still make this claim? Some peoples kids. When multiple, independent sources post results proving the motor, as tested, made MORE HP with the electric pump than the stock you have the unmitaged gall to make this statement?

    I'm not sure if you're angry that you never thought of this or just refuse to be proven incorrect.

    Hows this.. PROVE ME WRONG. Don't blather on about your thoughts. SHOW ME DATA, you're suppose to be an engineer.
     
  17. May 19, 2019 #137

    Kyle Boatright

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    If a guest came to my house and exhibited pfarber's attitude and lack of civility I would call him to the side and discreetly point him out the door, never to return. And I wouldn't lose a second of sleep over it.

    Problem solved.
     
  18. May 19, 2019 #138

    poormansairforce

    poormansairforce

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    My logic??? Dude, I quoted your resource that you posted!

    In case you don't get it yet, I used your hammer on your head! Again!
     
    Last edited: May 19, 2019
  19. May 19, 2019 #139

    pfarber

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    Having an opposing view is not lack of civility.
     
  20. May 19, 2019 #140

    pfarber

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    You asked me to show you your error. I did. You still don't get WHY you're incorrect. Just rest assured that you are.
     
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