Need Help! Need Advice For Super Charger On 03 Gt

Discussion in 'SN95 4.6L Mustang Tech' started by danno, May 17, 2014.

  1. The volume of the fenderwell or under the hood doesn't matter.

    For a given barometric pressure and humidity, temperature will define the density. For a given volume, what must change is mass.

    Air density is approximated by p = P/RT where p is the density, P is the absolute pressure, R is a gas constant and T is absolute temperature. Assuming 101.3kPa barometric pressure (P), a gas constant of 287.05 for "dry air" and a temperature of 25oC, the density of air is 1.184kg/m^3.

    So let's assume that the air we pull in from the fenderwell is at 25oC. Every cubic meter of air the engine pulls in will have a density of approximately 1.184kg.

    If we up the temperature of air being pulling air from under the hood that's at 65.6oC (150oF). Now the density of that same cubic meter of air is only 1.042kg. This is a difference of 0.l142kg or 12%.

    12% less mass means 12% less constituents, one of which is oxygen.

    Right, but this situation is not like the air in an automotive intake tract because you're allowing pressure to increase in the bottle while mass and volume are artificially constrained, mass particularly incorrectly. The barometric pressure at the inlet to the intake tract is comparatively constant over the range of temperatures. It doesn't really change much from 101.3kPa whether it's -20oC or +60oC. We know the volume consumed by an engine is fixed (swept volume, VE etc) so if temperature varies then the mass of the volume consumed by the engine has to change. See above.

    Hotter air is less dense air, less dense air has less oxygen with which to burn fuel and thus it has less power producing potential. This is why inter- and aftercoolers exist.

    A 13% reduction in the mass of air from pulling in 150oF underhood air versus 70oF ambient air will result in a power loss and it will also make an engine more prone to detonation.

    Gale Banks agrees:
  2. I do believe you when you say your car ran good with temps that high. But I'm also saying that it would run better, faster, and you could get more out of it if your temps were lower. Cooler intake temps are just better and will always be better.
  3. Alright, bear with me here.

    It's been quite a few years from my chemistry and thermo classes, and was never my strong point anyway. All of your stuff seems correct, and I can't [currently] argue against any of it. However, I'm still not convinced that it makes a significant difference.

    First of all, are your temperature numbers correct? Did you miss some decimal points along the way or anything? You say "250C" when I think it's supposed to be 25C. Same with the -200, 600, 1500, etc. Also, you are doing your calculations with absolute temperature, right? Missed more than a question or two on tests back in the day by using Celsius or Fahrenheit, haha.

    So let me start here. Temperature, volume, density, none of that actually matters when we're talking about power. The only thing that matters is mass (of oxygen) flow rate. Get more oxygen mass in a given time, and make more power. Agree?

    You made a comment about intercoolers; let's talk about that since they're a little more constrained (from a thermo/theoretical standpoint) than just fenderwell vs. underhood. An intercooler surely cools down the air, and via your reasoning earlier (which I can't currently argue with), the density increases also. This cooler, denser air makes more power (supposedly).

    But wait, we just said that increasing the oxygen mass flow rate is the only way to increase the power, right? Is the mass flow rate of the air entering the intercooler (which is hot) not the same as the mass flow rate of the air leaving the intercooler (which is cool)? If not, then do we have a mass-generating intercooler? Where is the extra mass flow rate coming from?

    If there isn't a better mass flow rate, and if the tune doesn't change, then where does the extra power come from? This is why I don't think the cooler air actually contains more oxygen.

    I think about this with my car. I have water/meth injection to cool my ACTs. They'll be in the 210-230 range with no water/meth, and come down to the 100-120 range with the water/meth. By your thermo work above, there should be a density, and corresponding mass, and corresponding power, increase with that temperature reduction. (Mind doing the math to see the difference there? Like you did earlier with 1500 vs 700?) But, my real world experience with the car is that that isn't true. It doesn't pick up any extra power with the cooler air and tune locked. I have done this experiment already. It runs a max of about 12 degrees of timing with no water/meth and 200+ ACTs. If I spray it, bring those ACTs way down, but leave the tune at that 12 degrees of timing, it doesn't pick up any power. None. It will actually lose a tad because of the slight enrichment from the methanol. The reason it picks up power, and the water/meth injection is worth it, is because I can run 24 degrees of timing with the cooler ACTs, versus the aforementioned 12.

    See my reasoning and logic here? I can't prove it currently through thermo equations and stuff, but my actual experience suggests that this cooler air doesn't actually have more oxygen in it. Cooler, and allow for more timing? Sure. But more oxygen content? No, not convinced yet.

    Also, that Banks article, you did read the last paragraph, right? ;)

    Agreed 100%, because you can run more timing with it. But as per my novel above, I'm not convinced [yet] it necessarily has benefits otherwise. :)

    Oh, and another picture (not mine) of the Fox I mentioned earlier from the track. DO WANT. :drool:

  4. Sorry for the misunderstanding. My temps were displayed "25oC" not "250C", the difference being 'o' vs '0'. The former was intended to denote "degrees" as in "degrees C".

    And yes, the equations require working in Kelvin (where zero Kelvin is equal to -273.15oC).

    When dealing with gases like "air" you can't divorce these parameters. You can't care only about mass flow rate without accounting for the other terms. But I agree that if you supply more oxygen and a commensurate amount of fuel, you will make more power.

    Well, not "supposedly", "actually." Intercooling and aftercooling have been proven for decades to improve performance on turbo- and super-charged engines.

    Conservation of mass applies but the parametric make-up of the charge on either side of the intercooler are quiet different from a temperature (intercooler removes heat), pressure (there's a pressure drop across the intercooler), velocity (slower on the outlet side of the intercooler), density (higher on the outlet side of the intercooler) etc.

    This isn't unusual. Think about airflow through a carburetor venturi: As it passes through the throat, the air speeds up and its pressure drops (resulting in fuel being drawn into the stream) yet the mass flow (excepting the addition of the mass of the fuel in the stream now) remains the same.

    :shrug: Cooler air is denser air and denser air, by definition, has more oxygen per unit volume.

    By injecting w/m into the airstream, you pull heat out of the air as the w/m vaporizes. A column of air moving through a pipe will be slower, cooler and denser after the w/m injection point.

    So for case 1 (no w/m):
    Let T=220oF or 104.4oC or 377.6K
    Let P=202600Pa (so assume you're running ~14.7psig boost )
    R = 287.05

    Density = P/RT = 202600/(287.05 * 377.6) = 1.87kg/m^3

    If we reduce the temperature (and realize that this approximation doesn't account for the change in the charge composition with the addition of the partial pressures of water and methanol and so is only a rough approximation...)

    Case 2 (w/m, assumptions made):
    Let T=110oF or 43.3oC or 316.5K
    Let P=202600Pa (so assume you're running ~14.7psig boost )
    R = 287.05

    Density = P/RT = 202600/(287.05 * 316.5) = 2.23kg/m^3

    This is an increase in density of 0.36kg/m^3 or 19.2%.

    But again, keep in mind that we're only approximating here and making assumptions. For example, R, the gas constant, assumes "dry air" (which w/m-injected air most certainly is not...) and there's a mass addition thanks to the w/m etc etc.

    If your tune is "locked" can we assume you're not adjusting fuel to optimize both cases?

    Curious: What was your AFR before and after?

    Well, the physics is sound: cooler air == denser air == more air per unit unit volume == more oxygen per unit volume.

    Issues of tuning and spark advance and how that extra density is utilized is sort of anecdotal and "ymmv".
  5. I see. I didn't notice that was a degree symbol, and not a 0.

    And why not? The only thing that matters is how much mass of oxygen is entering the engine. The temperature, pressure, density, etc., none of that matters. This is evident by the fact that we have a MASS air flow meter. This meter doesn't measure or know the temperature, pressure, velocity, density, volume flow rate, etc., only the mass. Because that's all that matters.

    They absolutely do. But they do so by allowing better combustion characteristics in the form of better spark timing and/or leaner air/fuel mixtures. They don't increase the mass of oxygen entering the combustion chamber. Only the power adder can do that (via more boost). But unless you change the pulley on the blower or have a MAP regulated turbo (regulated after the intercooler), then the mass it moves is going to be relatively fixed by things happening upstream.

    If conservation of mass applies, then how can there be more oxygen reaching the combustion chamber? To increase mass into the chamber, there has to a mass increase out of the intercooler. For there to be a mass increase out of the intercooler, there has to be a mass increase into the intercooler. For there to be a mass increase into the intercooler, there has to be a mass increase out of the blower. And for there to be a mass increase out of the blower, there has to be a mass increase in. With a blower, that mass uptake is relatively fixed by how fast it's being spun. And by a non-MAP regulated turbo, that mass uptake is also relatively fixed. So there's no way there's a mass increase at the chamber with the addition of an intercooler (assuming everything before it is being held constant).

    Agreed. But I still don't think more air is reaching the chamber because of the denser air. Maybe since the volume flow rate is less after the intercooler (mass flow rate = density * volume flow rate), then the VE across the heads is less? :shrug: I don't know, that's what I'm struggling to explain theoretically, but I still don't believe the mass flow rate into the chamber is actually changing (assuming you don't change the speed of the blower or turbo).

    Numbers all look good. But 19.2% is ridiculous. My car made 360 rwhp on the dyno last fall with no water/meth. 19.2% would be 70 extra rwhp. And that's not happening. Not even close.

    The commanded AFR was the same. But the MAF meters the incoming air mass, and then commands a corresponding amount of fuel to meet that AFR. So if the oxygen mass coming across the MAF actually increased, then the computer would add the extra fuel to keep that AFR, and the extra power should be present.

    Matter of fact, if you'd like, I can go do a little datalogging. I can datalog MAF counts both with and without the water/meth. If the mass flow does increase, it would be evident via the MAF counts.

    Commanded AFR is 12:1. At low rpm, where the amount of water/meth injected is higher per engine cycle, it richens up around half a point. Up nearer redline (6500 rpm), it's only a tenth or two. The water, being non-reactive, doesn't change the AFR. Only the methanol does that. And I'm only spraying a 75/25 mix of water/meth by volume, which is even less than 25% methanol by mass. So it's not a lot relative to the amount of gasoline being injected.

    I agree, but I still feel like there's something we're missing. Don't know what it is. Maybe the cooler air post-intercooler induces changes back upstream that allows more air to be brought in? :shrug:

    And throwing this back to the cold air intake debate, I look at it just like the intercoolers we're talking about, except in reverse. Say we're pulling in "hot" air from the underhood. For every pound of "hot" air pulled out of the underhood area, it has to be replaced by another pound of air. Where does that air come from? Yup, the atmosphere outside that underhood (which is at ambient temperature).
  6. Not all cars utilize MAF meters. Speed density cars use throttle angle, RPM, VE tables, barometric pressure, intake air temperature to compute the amount of air entering the cylinders to come up with a BPW.

    And even with MAF meters, temperature, pressure and density do matter; the meter is calibrated to reflect the mass of air flowing at any given moment as it reacts to all of these "unseen" parameters.

    And what about intercooled turbodiesels using compression ignition instead of spark timing? They benefit hugely from charge cooling.

    Well, in fact they do. I don't know how much more I can say on this. Cooler air is denser air and, as I said before, denser air by definition has more oxygen per unit volume.

    It does. I've already explained that while mass is conserved, the values of other parameters of the air stream are not assured to be equal on either side of the heat exchanger. Mass flow rate ~= V x d x A (velocity, density and area) and density, as noted, is approximated by P/RT. So, in essence, MFR ~= V x (P/RT) x A: The characteristics of the air stream ahead of the intercooler and after it can be markedly different in terms of temperature, velocity and density even as the mass flow rate is conserved.

    Well, what you believe flies in the face of decades of mechanical and chemical intercooling theory and practice.

    Bell Intercoolers engineers and makes these things. On their FAQ:

    "What is the purpose and/or advantage of an intercooler?
    The purpose of the intercooler is to remove the heat in the air charge that the turbo/supercharger puts into the charge when compressing it. There are two advantages: Reducing the heat in the air charge increases the charge density (more molecules of air per cubic foot), thus increasing the potential for making more power. Reducing the heat decreases the tendency of the combustion process to knock (detonation).

    And FWIW, I agree that a cooler charge reduces the propensity of end-gasses to detonate allowing one to run additional spark timing which will help power but the gains from increase charge air density can't be ignored.

    As I said, it's an approximation for the sake of discussion. But FWIW, a number of online sources indicate that gains of 15-20% with w/m in boosted applications is possible with all optimizations made.

    Snow Performance makes w/m systems. On their diesel FAQ they write:

    "Power is increased through:

    Air charge cooling - Water/methanol usually lowers air charge temps over 200 degrees F. Low air temps makes denser air charge which provides more molecules of oxygen for combustion.
    • Combustion conditioning - the methanol acts as a combustion catalyst as well as a cooling agent. Water vaporization inside the combustion chamber increases torque and power output through "the steam" effect.

    But that air immediately becomes heated when it contacts the AC condenser, the radiator, the piping-hot engine and manifolds. It makes more sense to induct air from the cool, ambient surroundings than to suck air that's been pre-heated under the hood.
  7. For Christ's sake, this has turned into an episode of Bill Nye the Science Guy gone bad. Just f*cking Google it. lol
    danno likes this.
  8. But the exact value of any one of those parameters doesn't matter. The only thing that matters is the total combination of those parameters. P1, T1, and V1 can be completely different from P2, T2, and V2, but if they both come out to the same mass flow rate, then they will be treated equally by the sensors and tune in determining how much fuel to throw at it. Hence, the mass flow rate, and ONLY the mass flow rate is what matters. There could be a thousand different ways of that mass flow rate manifesting itself, but the meter will treat them all the same way.

    They have timing, too. Timing of the fuel injection.

    And the density certainly is increased in that example, as it is regulated to maintain a certain amount of boost post intercooler. But that increase in airflow to the chamber is due to the fact that the turbo is spinning harder.

    If the mass is conserved (as you agree), then how can the intercooler itself increase the mass air flow!? The velocity and density before and after are irrelevant.

    However, you've got me thinking: since the velocity / volume flow rate decreases, what effect does that have on the mass of air going into the chamber? We agree that the volume flow rate decreases across the intercooler. Would that not have to have a negative effect on volumetric efficiency? Let's say the motor is displacing 400 CFM (swept volume). That's a fixed number, no changing it. With no intercooler, let's say the power adder is supplying 700 CFM, resulting in a VE of 1.75. But add an intercooler, with no change in the power adder, and that 700 CFM falls to 600 CFM, then the VE is only 1.5. We know the volume flow rate has to decrease by the same amount (proportionally) that the density increases per the conservation of mass (mass flow rate = volume flow rate 1 * density 1 = volume flow rate 2 * density 2; 1 being before intercooler, and 2 being after).

    Is any of this not true? And if so, wouldn't that account for the mass flow rate not changing, and thus no extra power?

    Now, the way you DO increase the power is to bump up the output from the power adder to get that 600 CFM back to 700 CFM, but now at the higher density. This certainly results in a greater power output, and I haven't disagreed with this at any point.

    Let's do this. Positive displacement blower. By definition, it moves a fixed volume per cycle. So the mass flow rate going through the blower is equal to the displacement volume of the blower * rpm * density at inlet. Agreed?

    Since the density at the inlet is fixed by the constant ambient conditions, and the volume flow rate is also fixed, then the mass flow rate across it is also fixed at a given rpm. Agreed?

    So now explain how cooling the air down, AFTER the blower, which is moving a fixed mass of air per unit time, can possibly increase the amount of oxygen moving into the engine? I welcome Bell Intercoolers, engineers, college professors, or John Force to explain where I'm mistaken. Maybe I am mistaken, but I don't see it.

    The same principle can be applied to a non-MAP regulated centrifugal supercharger or turbo, assuming it stays at the relatively same spot on the compressor map, which it will since downstream changes don't affect them much.

    I personally see upwards of 20% gains on my car when I throw the timing at it. But that's because combustion event (and corresponding pressure spike) occurs closer to the crank angle where the geometry of the rod and crank arm allow for a greater torque to be produced on the crank.

    But for every pound of air pulled from the underhood, it's replaced by a pound of air from outside (conservation of mass, no?). And since the volume of the underhood is fixed (I mentioned this several posts ago), the density (fixed mass / fixed volume) has to be the same, hot or cold. The only way it'd change is if the ambient atmospheric changed.

    I don't understand where my reasoning is wrong above, or how it can coincide with your "density = P/RT, therefore, higher T = lower density", but I'm certainly unable to argue against that.

    I have already. Both sides of this argument can be found all over. And I'm not very good at explaining why my side is correct, but with my real world experience, the other side has not convinced me yet either.

    And I assure you, the people who understand these things pretty much always have cars that run better, for less money, than those that don't.

    Not to mention, I freakin' love talking about and debating these things. :D It's not common I run across someone else who can.
    restomod66 likes this.
  9. Ha, a quote from Kenne Bell, of all places.

    restomod66 likes this.
  10. Agreed. Everyone should stick to the quotes they find on the web and their opinions and be done with it.
    restomod66 likes this.
  11. My sarcasm radar may need calibrating, but it wasn't my intent to piss you off (if you are).
  12. So wait a minute. Are we arguing whether or not colder air makes more power than warmer air? Because it seems like that's what the discussion is about. I don't see how anyone could say that warmer air is better. I mean, these are obvious facts. Why do we need scientific explanations?
  13. But they're not obvious facts. Go back and read either of my last two posts (minus the sarcasm one).

    Nowhere have I said or implied that warmer is better. Of course cooler is better because you can run more timing, a leaner mixture, or more boost. Duh. I have said that several times now. But I still think I've got a legitimate argument that cooling the air via an intercooler or water/meth AFTER THE FACT does not have an effect on the amount [mass] of oxygen entering the combustion chamber. If you can bring a scientific argument against this:

    Or this:

    then please do so. I'm well prepared to eat crow and move on. But I haven't seen it yet.

    Now bringing this back to the cold air intake debate, I think the above argument may could be extrapolated to the 'hot vs. cold underhood temps' debate also. My simple theory is that it's exactly the opposite of above: above, I say cooling the air down via an intercooler doesn't increase the oxygen mass in it, here I'm saying that heating the air up via the radiator/exhaust manifolds/engine block/etc. also doesn't decrease the amount of oxygen mass. I'll admit that even I'm a little less convinced of this, but again, I haven't heard an argument yet strong enough to convince me otherwise.
  14. Well sneaky, with all due respect, explaining the physics of it all is only gonna get you soo far. And soo far it seems to me that you guys are gonna keep going back and forth indefinitely. To be honest, all logic aside, you'd need a way of actually testing these things out to prove your point. Both of you would need empirical data. That's the only way a factual conclusion can be drawn from all this.
  15. Explaining and understanding the correct physics will actually get you everything.

    Don't worry, though. I'll get some data soon enough. My car's actually a good example, too, since I can change the ACTs with the flip of a switch. However, it looks like said data will be a little delayed; had a software error with my X3 the other day and had to send it back to SCT to get fixed. So will probably be at least a week or more before I get it back.