Help with GM maf or Speed Density

[cabot2g]

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

 

[crash89]

Im not familiar with either but am getting to know SD as I just got my car running on it and am still learning. I do know that if you want to go with speed density, you'll need to install a GM IAT sensor and a 3bar MAP sensor.. Here is a good write up on how to install the IAT sensor and log it via LINK.. http://www.dsmtuners.com/forums/articles-electrical-wiring/377567-wiring-logging-gm-iat-sensor.html Hope this kind of helps..

 

[gofer]

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.

 

[cabot2g]

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.

 

[WillRaceForBeer]

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".

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.

 

[gofer]

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.

The two most common GM MAF sensors used on our DSMs are the 3" and 3.5", part numbers 25180303 and 25179711, respectively. These sensors operate fundamentally different than the Mitsubishi MAF sensors. The GM MAF sensors work by measuring mass airflow directly. They do not need temperature and baro data because they're not measuring volume. They are reporting air mass directly as a frequency.

The biggest problem, IMO, with these MAF sensors is that this frequency to mass mapping is non-linear. So as airflow increases, it takes less and less change in frequency to present a larger and larger change in air mass. This makes the system very sensitive to fluctuations in frequency output from the sensor.

Neither a MAF Translator nor the ECMLink V3 GM MAF cable allow you to see the raw GM MAF sensor frequency directly. The MAF Translator provides a translation to stock DSM-like frequencies, while the ECMLink V3 GM MAF cable provides a simpler translation that produces raw frequencies that are quite different (but that the ECMLink V3 ECU code knows how to handle). So it's best to avoid talking about limiting-frequencies when discussing a GM MAF sensor when used on a DSM and rather just talk about air-mass metering capability.

Also, the GM MAF sensors, like any MAF sensor, are sensitive to anything that causes the airflow through the sensor to be unevenly distributed across the entire area of the sensor opening. It's very common to see smaller diameter piping leading to or from a GM MAF sensor cause the sensor to produce a higher airflow reading than that actual mass of air flowing through the sensor. Because the metering capability of the sensor is dictated by the maximum airflow reading it can report, having it report a value that is artificially high reduces the metering capability of the system.

That said, you can expect a 3" GM MAF to easily measure (report) 600 gm/sec (80 lb/min) well before any "limit" is reached. The 3.5" would probably measure over 700 gm/sec (92 lb/min)! The problem is that we have very little data to back any of this up. But the bigger problem, again, is that well before you reach these limits, the frequency to airflow mapping will simply become too sensitive to be usable. The result is a very choppy airflow signal to the ECU and many of the same problems mentioned above with MAF overrun on a Mitsubishi MAF. It's just for a different reason.

So with that in mind, we typically recommend that ECMLink users enable the MAF Clamp function with running a GM MAF. Enable it around, say, a MAFRaw reading of 2700-3000hz (that might vary a bit depending on whether you are using a MAF Translator or an ECMLink V3 GM MAF cable) so that the MAF signal is effectively ignored above that frequency anyway and it won't matter what's going on with the signal. This also effectively removes any metering limit that might have existed.

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

 

[WillRaceForBeer]

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

The stock MAF measures 3 things
AIR VOLUME / AIR TEMP / 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.

So anyone who says that air temperature affects the MAFT reading does not understand how it works. The MAFT takes into account high temperature and low temperatures by calculating MASS, not volume.

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.

 

[crash89]

Easy now children!!

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

 

[gofer]

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.

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...

I have my fans hooked up to the ignition switch. The fans are always on constantly. It's pretty crazy when you start the car up for the first time of the day and the coolant temp gauge is already creeping up to the normal range.

As for the "Intake Temp.", this has no effect on the ECU fuel delivery??? By running rich, I meant I saw my wideband in the 10.9s when in the cooler days it was hanging around 11.2s. I never knew the MAFT had it's own temperature sensor.

Wow, a whole 2.7% difference. 115 degrees F instead of 75 degrees F would be a a reduction in air mass of a little over 7%, so if the change in air mass wasn't reflected in the signal from the GM MAF, the A/F ratio should have gone down to 10.4:1.

The GM MAF doesn't have a temperature sensor. It measures air mass directly, unlike the stock MAF sensor which mreasures air volume, temperature and pressure which the ECU uses to calculate mass from PV/T (T is absolute temperature). Since the 'V' supplied by the MAFT is already mass rather than volume, pressure and temperature values have to be held constant so the mass value is not altered when the ECU plugs it into PV/T.

Dave

The GM ECU still may be using intake temperature to adjust fuel or timing to some extent, but not in the way the Mitsubishi ECU does to determine air mass since the GM MAF directly produces an air mass signal instead of separate air volume, pressure and temperature signals.

Dave

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.

 

[WillRaceForBeer]

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 translates the signal for the stock ECU. So, in that case, the ECU can account for air temp and baro using a GM MAF because of the MAF Translator.

Not at all what I'm talking about here, though. The ECMLink GM MAF cable plugs directly into the stock MAS connector to the GM MAF and, yes, you lose IAT and baro readings because there's no translator. That being said, tuning a car running a GM MAF can be tough because the tune can change day to day.

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.

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:

GM MAF and IAT

We get asked fairly often why we do not provide (or could we provide) IAT compensation for GM MAF sensors. The bottom line is that it's simply inappropriate to do so.

The GM MAF sensor does not require IAT compensation because it works in a way that takes air temperature and pressure into account automatically. This is the reason we provide an option to lock the IAT/Baro inputs when running with a GM MAS, thus freeing up both those inputs for other logging purposes.

This page is intended to provide some "proof" in the form of a couple datalogs illustrating how insensitive to varying air temperature the GM MAS really is. Both logs were captured on the same car on the same day using the exact same GM MAS.

One shows the engine running with air temperature in the 65-70F range while the other shows air temperature in the 160-170F range! The air temperature sensor on this car is located only inches away from the GM MAS.

Despite the large swing in air temperature, the GM MAS reading was nearly identical between the two logs. Fuel trim variation was less than 1% between them.

IAT near 65F
IAT near 165F

Hopefully this provides some reassurance to folks that the GM MAF sensors really do not require and would not benefit from additional IAT compensation. In fact, since the GM MAS signal is already accurate as air temperature changes (see datalogs), providing IAT compensation would actually mess the signal up.

So basically, we don't provide IAT compensation on a GM MAS because it simply doesn't need it.

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

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.

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!

 

[cabot2g]

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...

 

[gofer]

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.

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.

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]

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.

 

[WillRaceForBeer]

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

 

[gofer]

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

 

[cabot2g]

Thanks for your help guys!

 

[liquidsilver]

Great info in here.

Back to the drawing board...

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.

 

[cabot2g]

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.

 

[96 420a-t]

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.

 

[JeffGST]

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.

I have my fans hooked up to the ignition switch. The fans are always on constantly. It's pretty crazy when you start the car up for the first time of the day and the coolant temp gauge is already creeping up to the normal range.

As for the "Intake Temp.", this has no effect on the ECU fuel delivery??? By running rich, I meant I saw my wideband in the 10.9s when in the cooler days it was hanging around 11.2s. I never knew the MAFT had it's own temperature sensor.

JULY 2005

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

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.

 

[obsidian]

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.

 

[daren_p]

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.

 

[angelito2g]

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

 

[ghostd'GST4life]

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!

 

[cliffkemp]

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.