what exactly is dynamic air mass

 

well dynamic airmass/airflow is what the calculation of airflow that is contributing to combustion. It's part of the VE equation the PCM goes through... I think... lol Check out one of the stickies at the top of this forum!

 

On my "Dialing in MAF tables Anyone?" thread I posted my results and step by step of what i did. Look the thread through and through, and disregard the 2nd topic that sprung off it, but based on all the discussion, I believe this would be the best way to do it! I need a beer but I'll be back around 1:30 central time, IM me if you wanna talk about it! I have thought out alot of the "physics" and tried to relate it to motor operation so I can probably answer a # of your Q's

Also, i offered to make my procedure a "sticky." Look it over and lemme know if you think it's sticky worthy.

 

yeah i have been reading it but it was so much, now that u changed it ill go check that out

 

Man, probably I'm not the only one getting an headache rading this post... Joke

MAF measures MASS per TIME UNIT (gram per second for my metric thinking head).
No matter which altitude, no matter which temparature or pressure.
It's mass.

for tuning log MAF frequency, mass air flow rate, cell, LTFT.
drive first 30 before start logging
drive in all possible conditions
take only cells 0 to 15
average B1 / B2
Round up the frequency so that the numbers are the same as in the MAF curve
put frequency and LTFT in a pivot table and you'll see which frequency will have to be changed (I personally aim to -1 LTFT)
make a smooth curve
redo the job a couple of times until the load cells are negative and cell 22 at WOT will be = 0

...it works fine if the VE table is correct, if not start with it first or the MAF tuning will be a mess...

 

the mass flow rate equation is directly effected by presure and indirectly effected by temperature. mass flow rate is kg/s, or what ever unit you choose. density is kg/m^3 and volume flow rate is m^3/sec. multiplying the 2 the m^3 cancels and u are left with kg/sec. the density could be considered a constant but only in ideal cases. we will never see an ideal case as you know so the density is constantly changing.

which brings this up. i wonder if the intake air temp sensor (IAT) is used in determining the MAF values. if this is the case the only difference that would effect the calculation would be the baromertric pressure, which changes could almost be considered negligable. this would allow for better tuning.

i will have to talk with txhorns and try and understand VE a little better. maybe this will play a factor into only a certain percentage of the desired MAF rate is the actual desired rate. i will also discuss this when i get a chance, when my thermo 1 professor. he is in the motorsports division at our school and im sure he will know a lot about this. time to get ready for class now though, ill try and read txhorns post, maybe that will help me think some more

 

a quote from cracked ve tables:

I have been working on the VE table quite a bit lately and I think I found the solution.

Thanks to gameover for some key hints.


The VE table looks as though it is in meters cubed, it is just not used like a conventional VE table. The VE values are such that the PCM can directly backcalculate to g/cyl, the primary means to determine fueling and timing.
This is what makes it so confusing. You can't solve for air mass, you have to solve for g/cyl.

Anyhoo, here is the equation

VE = ((massflow * IAT / (MAP * RPM * Displacement))

Massflow: grams/sec
IAT: Degrees Kelvin
MAP: Bar
RPM: Duh!
Displacement: Cubic Meters

To solve for the massflow in g/sec simply re-arrange the equation.

Massflow = (VE * MAP * RPM * Displacement) / IAT


My old method of "Divide by 30" works okay because we are inadvertantly solving for a volume ratio. The molar mass of air is 28.96 g/mol.


I have compared the above equation to every bit of data that I have ever collected for a stock car, and the data matches up perfectly.

Any corrections, comments, or blinding errors please let me know.

Thanks,
Kevin

ok if someone could explain to me what getting this number does it would really help, ill read through the thread in my break at school. the mass air flow seems to be the only one not known, but if it is calculated and you knwo what the motor has to have then we sould know what the ve should be, only thing is i dont know what it matters having this number. i should be getting hp tuners soon so that should help actually having it. txhords seems to be the man, so let me knwo when u get on here next lol

 

this is what my thermo 2 professor told me in email:

Most of what you have said is correct. The air density can be obtained
from
the ideal gas equation of state. You will need the volumetric
efficiency
for the engine versus RPM. That is how well the engine can fill the
cylinders and is related to fluid flow losses in the intake tract.

GJM

now if we can figure out that variable, dont know if it could be obtained the same way as in the previous post, then we can figure this out. also, if the IAT is actually used for MAF which i would assume it is.

now from what i have read the VE table takes the actual MAF and determines how much is being used for combustion, and this is why the LTFT's come into play right? it will determine if more or less is contributing.

right now the only thing i can really think of to get accurate VE is to return the MAF and its table to stock and do a SD tune. this will get the VE table correct and then take the factory MAF readings (assuming they are accurate left in stock trim) and dertermind the VE at each rpm level. then this could be applied to the MAF theoretical and find the MAF actual and making a table from that, maybe?

http://www.installuniversity.com/ins...n_9.012000.htm

this is a pretty good link right here

ok so we can determind the VE now from that equation. i would think that a trial and error testing, getting the car right at 0% for the fuel trims, would mean the VE tables would be more accurate. if you calculate i would think there could be some very small error in there. there is uncertainty in each factor, although it is most likely negligable. so we have the VE table set, we knwo the VE of the motor and we can figure out how much of the theoretical mass air flow is comming in, due to the restrictions on our motors ie. heads, cam, and what not. then the MAF table could be built from this. we would need:

MAF values
IAT values
MAP values
RPM values

to get what we need, unless i left some out, and may have. i would think from this a MAF table could be built. my head is starting to hurt now so im gonna rest before i have to sit through an hour of dynamics haha.

sorry i have been editing this to keep the posts from going way up, so if i contradicted myslef in here let me know and ill fix it, im rereading it right now.

 

ok let's drop the science for a sec and think about this, your MAF (the electronics themselves) don't really "see" or calculate anything. It measures frequency, end of story. Based on what frequency it measures it will go look up the airmass in your MAF table to deliver to the PCM. THis airmass value is a user input, so however you calculate it, then it's up to you. BUt that seems a little complicated to me. I know that the motor already does it's own calculation of what it wants/needs/expects as far as airflow goes, in its VE function. So if we want as little MAF discrepancy and bias as possible, we align these two, as in we calibrate the MAF according to what airflow the motor is using for combustion (dynamic airflow), then using the dynamic airflow as a reference you can rebuild your MAF table. All you have to do is log dynamic airflow and MAF frequency.

Now since we've discussed that motor operation changes due to weather/road conditions, the MAF will not always be 100% perfectly aligned with motor operation since it is not adaptive. So the best way to manage this is either 1)Don't run a MAF or 2)Calibrate your MAF in what you would consider medium type weather in your locality, that way the MAF will at least be centered as far as general motor operation.

NO MORE PHYSICS!!!

 

yeah that is esentially what i am saying, the dynamic, actual air flow, vs MAF. we are just speaking in 2 different languages i think lol. the maf measures the velocity of the air right? it then uses that to look up what the airflow is in a table. we could tell the computer what that airflow should read out for that certain velocity and speed. i think we are talkin about the same things u are just going by logging and making the table andim going on calculating the table. but the same thing now that i think of it lol

 

I don't think the IAT has a rule in the air quantity calculation: the MAF is a standalone MASS AIR meter. The resistances in the MAF flow are cooled by the mass of the flowing air. No matter at which temperature, pressure or whatsoever. Mass is mass. Humidity plays a rule but not in our "not really precise" application. In the industry it's mandatory to dry the air prior going through such a meter - not realistic for a car.

VE using the MAF: using thid method I was 10% too high - it was using the stock filter and stock MAF calibration.
In the industry (yes, again) you need a straight pipe long at least as 5 time the diameter of the meter to obtain a laminar flow (necessary for this kind of meter). Just a little turbulance and the measurement is no more correct. We don't have so much space... Our MAF screen produces a laminar flow but in my opinion it's not perfect.
I prefer the O2 method: those sensors are very accurate and will give you all the necessary informations you need to determinate your VE and a nice MAF curve.

Look here for a nice explanation:
http://www.hptuners.com/forum/YaBB.p...num=1100894562

I agree with txhorns281: the car uses several signals to determinate the best setting: mostly VE and MAF. Depending on the situation the PCM will use more the VE or the MAF. If both signals give the same result the car will be "happy" and respond "happily". If not The PCM will have to decide between two different signals: the result is a bad response.

 

Well i'd say the more variant the two calculations of airflow are (b/w MAF and motor) the worse the response! But you got the basic idea down!

 

what i was saying is maybe the temperature of the air is relayed to the computer in the computation. not saying it was but i was just wondering, why else would it be there, in front of the MAF? yes mass is mass but the characteristics change with conditions. you have to take the density of air into consideration for the calcualtion, and that is variable depending on conditions. the mass flow rate will change with temperature, pressure, and vapor pressure. i dicussed this with my professors and it is not just mass is mass. the role is not humidity is the pressure of the vapor, this is a number that is calcualted based on temperature. the reason that VE is taken into effect is that this is not stead state, steady flow, you have to take into consideration flow work and bends and twists into the system. this is what the VE will do, when you find this % multiply it by the MAF and you have the demanded air flow of the motor.

i agree that the VE should be tuned off the o2's because that is more accurate but the maf is a constant factor, except for the density changes which MAY be accounted for by the computer. the only way is trial and error, i will test out my theory when i get hp tuners and post up what i determined from this. the VE could be determined from simple calcualtions and numbers found in the table, a curve could then be fit and adjsuted on for optimum numbers. im still in the research of this and i have been in contact with some of the best engineering professors at UNC Charlotte. they know their **** so i gotta talk to them more.

although i disagree with some thing being said, i will take it all into consideration and present it to my professors

 

The IAT is ther for multiple reasons. It is critical in determining SD calculated air mass, which is used partially for fueling until 4000 rpms. It also affects yout ignition timing.

 

ok, so above 4000 rpm what is used? and how is the tuning done above 4000 rpm?? that is one aspect im not clear about, but im reading somethign right now maybe it will mention it

 

If you have a MAF, then your MAF is used (no VE included in calculating fueling). If you have no MAF it uses VE alone. And if your MAP fails the PCM switches to N-Alpha based on RPM and TPS. And if all of those fail call a tow-truck.

 

ok so above 4000 rpm is when the maf has to be tuned correctly, and below that it is a mix of maf and ve?? is that right?

 

You got it! VE for low load, MAF for high load and in between a combination of both.
A nice thing is to have a SD tune with all LTFT at 0 / -1% and a MAF tune with about the same values. My car now runs this way and it's much better then when I was messing around the classical way (IFR & PE).
Better response and better mileage too.

This of MAF, density, temperature and so on: I think everyone has to develope his personal way to explain things. As long you get a good result it's not important how you got it, it is important that you can explain it using your logic. Maybe it's not the reality but at least you see a relation between what you do and the result.

Physics, flows, temperature and those things are what I do for living and I have my personal way to explain what happens. It's not always the same as in the books, maybe it's not the reality but as long I got a result who cares? As long as the company pays me a salary to build chemical plants it's fine...

 

haha i got ya, im sure we are all talking about the same thing but te differences in the equations are the difference in our parameters, there are hundreds and thousands of ways to get to the same answers.

now what is pe for? isnt that for WOT tuning?

 

Your MAF needs to be correct at all RPM ranges, and your VE on a MAF car needs to be correct until at least 4000 RPMs. An incorrect MAF table will throw your trims off when it is still being mixed with SD, and vice versa.