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Help with GM maf or Speed Density

Posted by cabot2g, Apr 18, 2012

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  1. cabot2g

    cabot2g Proven Member

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    I have a question for the people running DSMlink V3.

    My son and I are building a 99 GST and I am having trouble deciding weither to run a GM MAF or Speed Density. I have DSMlink V3 lite and for now the car will be running a VTA BOV, (do not bash please). I have a GM MAF and was planning to use it but I do not know much about tuning or setting up Link YET.

    Would I be better continuing with the GM MAF or going with speed density?
    So far, all I have is the GM MAF, still have to get the cable and couplers, I will sell the maf if the SD is better/easier to install/tune.

    I have searched and read a lot on both but I am still unsure which route to go.

    Thanks for your help
     

    319  0

    1999 Mitsubishi Eclipse GST
    · 2G DSM
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  2. crash89

    crash89 Proven Member

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    Janesville, Wisconsin

    5K  4

    1999 Mitsubishi Eclipse Spyder GST
    awd · manual · 2G DSM

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    1999 Mitsubishi Eclipse Spyder GST
    11.043 @ 125.92 · 2G DSM
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  3. gofer

    gofer Moderator

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    South Gilbert, Arizona
    Speed Density and a GM MAF do the same thing, provide the ECU with airflow data, but each have a different way of doing it. So, generally speaking, I wouldn't say one is necessarily better than the other. The GM MAF can see a limit in airflow, however, we're talking 80lbs/min (700+whp) so it comes down to personal preference and cost, really. I personally found that Speed Density was easier for me to tune once I understood how it worked, there's just more "resolution" to tuning SD.

    The GM MAF can be tough, at least mine was. First, the GM MAF doesn't take changes in intake temp or baro into account so from one day to the next your tune can be "off"(This statement is incorrect after being linked to this page, please disregard Wiki: GM MAF IAT) . Also, standard IC pipe is 2.5" and the GM MAF's are 3 or 3.5" so you need to run a coupler that goes from 2.5" to 3" then a reducer that drops back down from 3" to 2.5". This increase/decrease in your IC plumbing can create turbulence inside the piping, specifically on the GM MAF, which can make tuning a bit of a headache, too. Read the bottom of this article regarding the GM MAF. ---> Wiki - MAF Frequency Limits

    Speed Density is a bit more involved if you plan on tuning it yourself, which leads to a lot of reading and re-reading if you don't understand it the first few times. It also requires some fabrication since you'll need an IAT bung welded in your IC pipe between the cold side of your IC to the TB. The MAP sensor install is fairly simple even if you've got a stock IM, RRE makes an adapter. (Just scroll to the bottom) 2g MDP/MAP adapter

    How should you pick which is better? That's a good question. How much money are you willing to spend and time do you want to invest (reading up on tuning) should be the deciding factor here. I think it would be a good idea to sit down and add up a end total cost for both, then see if that makes the decision for you.

    :dsm:
     
    Last edited: Apr 19, 2012

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    1997 Mitsubishi Eclipse GST
    11.634 @ 126.050 · 2G DSM

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  4. cabot2g

    cabot2g Proven Member

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    Thanks guys,

    I think I am going to go with the MAF, I already have a 3" maf just need to get the 2g GM MAF cable. I have been looking in the marketplace for one. Hopefully one will turn up soon.
     

    319  0

    1999 Mitsubishi Eclipse GST
    · 2G DSM
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  5. WillRaceForBeer

    WillRaceForBeer Proven Member

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    Joined Feb 7, 2003
    Fairfax, Virginia
    I just want to point out that this is incorrect, the GM MAF absolutely takes intake temp and baro into account DIRECTLY by measuring temperature loss across several diodes. As such a GM MAF does not provide intake temp or baro signals to the ECU, because the measured airflow already has temp and pressure factored in. Mass flow sensor - Wikipedia, the free encyclopedia

    As such the GM MAF is a great solution for daily driving and of course works great in blow through setup. SD is certainly a great option as well but does require a bit more learning and understanding. Of course dialing in a GM Maf does have it's challenges.
     

    618  0

    1995 Mitsubishi Eclipse GSX
    13.433 @ 102.280 · 2G DSM
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  6. gofer

    gofer Moderator

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    False. I wish people would READ as much as they liked to argue, then conversations like this wouldn't even happen. READ this link, which I posted above, and find the GM MAF Sensor info down at the bottom. --->ECMLink Wiki: MAF Frequency Limits

    Since that maybe too much work for you I just copy/pasted it below. :toobad:

    Anything else incorrect? Also, where in your Wiki link does it say that a GM MAF takes intake temp and baro into account?

    :dsm:
     
    Last edited by a moderator: Jun 5, 2014

    Street Build 18K  13  61

    1997 Mitsubishi Eclipse GST
    11.634 @ 126.050 · 2G DSM

    3K  0

    1997 Mitsubishi Eclipse N/T
    manual · 2G DSM
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  7. WillRaceForBeer

    WillRaceForBeer Proven Member

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    Fairfax, Virginia
    Gofer, you clearly do not understand how a GM MAF sensor actually works... and your post was spreading incorrect information. Please read this carefully.

    First ECMlink is absolutely correct, the GM MAF does not measure volume, what they don't say is that it measures AIR MASS.

    AIR MASS already has pressure and intake temp factored in due to the way the GM MAF measures AIR MASS.

    http://www.dsmtuners.com/forums/newbie-forum/287590-gm-maf-maft-changing-weather-conditions.html#post151444517

    Please do not accuse me of arguing until you understand what we are discussing. And please as a Mod be willing to READ and accept when you are wrong.
     

    618  0

    1995 Mitsubishi Eclipse GSX
    13.433 @ 102.280 · 2G DSM
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  8. crash89

    crash89 Proven Member

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    Janesville, Wisconsin
    Easy now children!! :p

    OP: Now I know you decided to go with the MAF set up but I just wanted to post this little info on top of Gofers post in post #3. Aside from going with the RRE adaptor for an AEM map sensor, Modern Automotive Performance provides a direct bolt in 3 or 4 bar MAP sensor for a stock 2g manifold!!! This is what I went with for my SD set up.. Omni-Power Mitsubishi Universal Map Sensor (3- or 4-bar) - Modern Automotive Performance
     

    5K  4

    1999 Mitsubishi Eclipse Spyder GST
    awd · manual · 2G DSM

    4K  10

    1999 Mitsubishi Eclipse Spyder GST
    11.043 @ 125.92 · 2G DSM
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  9. gofer

    gofer Moderator

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    South Gilbert, Arizona
    That's a great post by Jeff but unfortunately doesn't disprove anything I said, he's talking about running the GM MAF with a MAFT which locks the Baro/IAT itself, rather than at the ECU.

    After some research, the only GM MAF that has a built in temp sensor is a 3.75" which is bigger than the usual 3" or 3.5" GM MAF's DSMers run. When setting up a GM MAF on a DSM both the baro and intake air temp signals get locked, so any GM MAF tune would require some adjustment because of a change in temperature.

    EDIT
    Found this over on Link...
    So who's incorrect? Neither of us but since we're talking specifically about DSMs then it is true that the ECU can't account for changes in air temperature or baro when tuning a GM MAF. :)

    :dsm:
     
    Last edited by a moderator: Jul 10, 2014

    Street Build 18K  13  61

    1997 Mitsubishi Eclipse GST
    11.634 @ 126.050 · 2G DSM

    3K  0

    1997 Mitsubishi Eclipse N/T
    manual · 2G DSM
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  10. WillRaceForBeer

    WillRaceForBeer Proven Member

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    Your missing the point of why his post was relevant. The fact is that the GM MAF provides it's signal in terms of MASS, regardless of if you are using a Maf-T or a cable + dsmlink v3. Both solutions allow for proper interpretation of the signal from the GM MAF.

    Since you need proof, here is the proof, logs included, that the GM MAF compensates for temperature, climate, etc variations, straight from ECMLink:

    gmiateffect [ECMTuning - wiki]

    I ran a 2g MAFT for 3 years. I've been running v3 with a straight cable since early spring. Both solutions respond properly to climate change when dialed in properly.

    For those who may stumble across this thread in GM Maf research...

    Stock ECU calculates airflow using this formula: (Pressure * Volume / Temperature = MASS) Where pressure is BARO, Volume is HZ from the stock air sensor, and Temperature is IAT also from the stock air sensor

    GM MAF signal is simply the final value of that equation which is MASS, there is no math calculation required to adjust for climate factors.


    EDIT
    I think you're almost there, but the thing is, the ECU doesn't NEED to compensate, the GM MAF is providing a compensated signal, PV/T is already done :)

    The MAF T actually has to take a step backwards and prep the GM MAF's signal for our ECU which is expecting P,V,T instead of MASS, like you said it clamps P and T and translates V. DSMLink V3 was a step forward because it could handle the MASS signal by clamping P and T in the software, and of course MASS comes in as V and get's adjusted quite a bit by dsmlink. For example 600hz from a GM MAF = ~30hz that the ECU sees.

    Honestly I apologize to the OP for all of the back and forth, but whichever way you go, this is all good info to have when you start tuning!
     
    Last edited by a moderator: Jul 10, 2014

    618  0

    1995 Mitsubishi Eclipse GSX
    13.433 @ 102.280 · 2G DSM
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  11. cabot2g

    cabot2g Proven Member

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    I don't mind the back and forth. I know both work, just trying to come up with something that works well on a daily driver.

    As a side note I went back and read what V3 lite offers and I have to upgrade to the full version to run the gm maf stright to the ecu. Back to the drawing board...
     

    319  0

    1999 Mitsubishi Eclipse GST
    · 2G DSM
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  12. gofer

    gofer Moderator

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    I wasn't missing the point, I'm not a physicist so those equations don't mean much to me (at least when it comes to understanding WHY a GM sensor wouldn't need a temp sensor). All the research I've done I was under the impression that temperature/baro changes affected the tune. Personally, I saw this happen when I was running a 3" GM MAF because it seemed everyday my closed loop FT's would be off enough to need adjustment.
    Of course I need proof, especially after experiencing/seeing a change in closed loop FT's (when I DD'd the car) running a GM MAF. I have never seen that Wiki page regarding GM MAFs and I'm still not certain why, when you initially posted, you linked to a Google search Wikipedia page regarding MAF's in general. This thread would have only gone as far as a post immediately after your first and it would have said, "thanks for the link and correcting me."

    I wonder if my experience, regarding the changes in tune I was seeing day to day, was due to the quick increase in IC pipe size right on the GM MAF now that I know it can account for IAT and Baro.

    :dsm:
     

    Street Build 18K  13  61

    1997 Mitsubishi Eclipse GST
    11.634 @ 126.050 · 2G DSM

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    1997 Mitsubishi Eclipse N/T
    manual · 2G DSM
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  13. WillRaceForBeer

    WillRaceForBeer Proven Member

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    Wish I would have :) Just found that page myself. I learned most of what I know from the Wikipedia page, read the whole thing one day. The section on "Hot wire sensor" Maf's was relevant to the GM Mafs. I didn't have any direct supporting info until I found the ECMLink page.

    It's possible that the increase in IC pipe size before the maf could have disrupted the airflow a bit, but I think the most important thing is that it's a straight flow into the GM MAF. Anyway no way of knowing now, I presume from your numbers that SD is doing well for yah :thumb:
     

    618  0

    1995 Mitsubishi Eclipse GSX
    13.433 @ 102.280 · 2G DSM
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  14. gofer

    gofer Moderator

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    Well, at any rate, I do appreciate you correcting me and I apologize for being a knuckle head when you first linked to Wikipedia.

    :dsm:
     

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    1997 Mitsubishi Eclipse GST
    11.634 @ 126.050 · 2G DSM

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    1997 Mitsubishi Eclipse N/T
    manual · 2G DSM
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  15. cabot2g

    cabot2g Proven Member

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    Thanks for your help guys!
     

    319  0

    1999 Mitsubishi Eclipse GST
    · 2G DSM
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  16. liquidsilver

    liquidsilver Proven Member

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    Great info in here.

    Not neccessarily. The stock 2G MAF is good for around 400hp. So just keep that in mind along your upgrade path, and recirculate your BOV.
     
  17. cabot2g

    cabot2g Proven Member

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    Right now I dont have a bov that will recirculate or an intake that it can hook up to.

    I already have the gm maf, just need a translator.
     

    319  0

    1999 Mitsubishi Eclipse GST
    · 2G DSM
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  18. 96 420a-t

    96 420a-t Proven Member

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    Anothe option ( obviously not the best) is that the safc has an option to take into account the BOV releasing measured air in a turbo MAF system. Its not the best way but it will get you by, so long as your BOV is closed at idle.

    I ran a 1g BOV and while at idle it would hang open. Hooray speed density.

    And another side note an added benefit to SD is if something does happen say you hit something and rip a coupler or something it is possible to limp it home with out issues.
     
  19. JeffGST

    JeffGST Proven Member

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    I just found this thread today with my quotes all over it.:sneaky:

    The passage you quoted me on was written 7 years ago, when I was first understanding the operation of the MAFT. Even Dave (ECMlink Co-Creator) didn't even understand why the GMAF had it's own temperature sensor built into it at the time.

    The reason why the GMAF has a temperature sensor has NOTHING TO DO with the mass airflow calculation. The GM ECU uses the intake temperature data only for ignition retarding. If it used the temperature data for MASS calculation, it would corrupt the final MASS value.

    This is the only thing you need to remember with the GMAF.

    The stock MAF measures 3 things
    V= AIR VOLUME
    T= AIR TEMP
    P= AIR BAROMETRIC PRESSURE

    Then the ECU uses (PV/T = MASS) to calculate MASS.

    The GMAF measure only 1 thing. It measures MASS directly. So when the ECU receives it's signal from the GMAF it is measurement of MASS and not Volume. Therefore the Translator MUST hold barometric pressure and air temp constant so that the (PV/T =M) calculation is not corrupted. We already have M directly from the GMAF.
     
  20. obsidian

    obsidian Proven Member

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    This is way too complicated. Can I carb my 4G63 ###?

    For some reason p.l.z. was blocked but please?

    It is a joke BTW. I'm running the GM 3" Maf and my tune is way richer than before. I tuned it almost 8 months ago with link and now it's warming up again, I'm running pig rich.

    So, I want something where I'm not going to have to retune every 2 weeks to be properly adjusted.

    I grabbed my 1g MAF back and am HEAVILY considering reinstalling it. I DD the car so I'd want to have something reliable and still fun to romp on. I should be putting down close to 350ish so I'm on the fence. Can't find a local 2g setup and I'm broke.
     

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    1990 Eagle Talon TSi AWD
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  21. daren_p

    daren_p DSM Wiseman

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    I have no personal experience with a GM MAF, I've been running the stock MAF up till this point (clamped as I'm exceeding its limits) but will be making the switch to SD. All I know is there no longer seems to be alot of guys running the GM MAF, once SD became an option. I also remember how excited all the GM MAF guys were about SD coming out & they couldn't wait to switch, fwiw.
     

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  22. angelito2g

    angelito2g Probationary Member

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    rite now im going to run a speed density on my car. i feel that's the best way to go for tuning issues. Just my 2cents
     

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    1995 Eagle Talon TSi AWD
    · 2G DSM
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  23. ghostd'GST4life

    ghostd'GST4life Proven Member

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    Fall River, Massachusetts
    save up your money and go with speed density. In the long run it will benefit you more than a gm maf will, especially on a good tune!
     

    316  0

    1998 Mitsubishi Eclipse GST
    · 2G DSM
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  24. cliffkemp

    cliffkemp Proven Member

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    Just curious as to the 'argument' ....

    Would it be true to say that a MAF sensor that works such as a GM sensor does not need to know temperature and pressure due to the fact that at a given temperature and pressure, it is going to cool off the coils a 'certain' temperature and that is what the GM MAF is 'tuned' for.

    If the temperature is 32 degrees F and at sealevel, then the air will have a certain density based on a barametric reading and, this is the mass of the air so, therefore, if any variance arises....temp goes up/down, baro goes up and down, or any change, changes the mass of the air???

    Just throwing that out there. :)
     

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