what should I get with my dsmlink?

[pj91gsx]

very cool. When you say 3 bar is that 3'' MAF, is 5 bar a 5" MAF? What makes a GM MAF a certain bar rating?

[turbosax2]

You are confusing MAP with MAF.


GM MAF - comes in 3" and 3.5", referring to the diameter of the sensor.



AEM/GM MAP - comes in 3 bar, 5 bar etc., referring to how many bar (or psi) the sensor can read.

[pj91gsx]

oh. In that case, will a MAP replace the stock MAS, just like a GM MAF replaces the stock MAS? Which is better? So, a GM MAP is an upgrade to a GM MAF? Does a GM MAP need a MAFT to work?

[gsxtasy]

Alright, they are two different things. A MAP sensor doesn't relate to a MAF/MAS sensor. MAP just reads manifold pressure. The MAF/MAS reads airflow. You don't *need* a MAP for either a stock mas or gm maf, nor will it replace either. Unless your getting into speed density, which your not, and is a whole other can of worms. It's just a helpful tool to tell what your actual boost pressure is.

You can log a MAP sensor in dsmlink so you will have actual boost readings in your log, instead of just the boost estimate.

[pj91gsx]

I got it. thanks for all of the help. you guys are all such a big help. Thanks.

EDIT: is the boost gauge more accurate than the "boost estimate" from the stock MAF or GM MAF? The "boost estimate" does come from the MAS or GM MAF right?

[My1GLaser]

Thats a more complicated question than you would believe. I would recommend searching "boost est" on the DSMLink forums. You are a member there, right? The forum is freaking invaluable and you should search there as much as you search here because of the specific DSMLink help you can get.

Anyway, boost est is an "expected boost amount" based on quite a few factors. Basically, Link sees all the data coming in (airflow, hz, inj on, etc) and puts together the info and says "this is probably the boost you are running, right...?"

It is only accurate at 100% VE (volumetric effeciency) which is from 5000-6000 rpm on a 2.0 DSM. At no other point along the graph should you expect the boost est to be 100% correct and the same as your boost gauge.

This is why the MAP sensor is handy. You connect it to your intake and it reads the psi in there, which should be the same as your boost gauge. You can then log your actual boost psi in DSMLink and look back to see if it the same as boost est from 5000-6000rpm. Because I don't know about you, but it is a PITA to keep track of all this sh_t doing a 3rd gear pull to 90mph on the interstate.

Oh, yes the boost gauge is more accurate. Unless there are leaks or something wrong with it.

[pj91gsx]

Yes, I am a member of the dsmlink forums. I visited it once and was quite confused. I have heard of boost est and now it makes much more sense how you explained it. So, I should monitor the boost gauge on a 3rd gear pull from 2000 to redline, and I should read the boost gauge between 5000 and 6000 rpms. Then I look at my recorded run and adjust the Boost est to what I read on the boost gauge between 5000 and 6000 rpms right?

[My1GLaser]

Yes. If you can manage remebering the boost gauge psi while at 5000-6000 rpm in a 3rd gear pull that is what you should do. I have one f_ck of a time watching all that sh_t while flying thru 3rd gear on the interstate on-ramp.

If you are running a stock MAS they should line up within about 1psi. If they don't, then you have to go to that HZ and adjust the airflow slider accordingly. I haven't had to touch my airflow sliders using a 2G MAS. Now my GM MAS I used to run...thats a whole different story.

Lets use an example at 5500 rpm.

Boost est shows 20 psi.

Boost gauge reads 17 psi.

That is an 18% overestimation of airflow. So lets say that was at 2000 hz. You would move the 2000hz airflow slider down -18%. Now the ECU thinks you have 17psi worth of air (which you do) and it injects the correct amount of fuel. (for either your targeted A/F ratio or the stock A/F ratio)

[gsxtasy]

Check out Jeff's site, it has a bunch of useful info on it. Here is the maf calibration page, good read.

http://jeffgst.com/gmafcalibration1.html

[scottsee]

Hu, My1glaser you did a good job explaining that..

[JeffGST]

Originally Posted by My1GLaser

Lets use an example at 5500 rpm.

Boost est shows 20 psi.

Boost gauge reads 17 psi.

That is an 18% overestimation of airflow. So lets say that was at 2000 hz. You would move the 2000hz airflow slider down -18%. Now the ECU thinks you have 17psi worth of air (which you do) and it injects the correct amount of fuel. (for either your targeted A/F ratio or the stock A/F ratio)

Originally Posted by scottsee

Hu, My1glaser you did a good job explaining that..

Except for the fact that the calculation was wrong.

BoostEst = 20 PSI
Actual Boost = 17 PSI

That is an -8.65% overestimation of airflow.
((Actual Boost + 14.7 PSI) / (BoostEst + 14.7 PSI)) - 1.0


((17+14.7)/(20+14.7)) - 1.0 = -8.65%

Straight off my website. http://www.jeffgst.com/gmafcalibration1.html

He forgot that planet Earth has it's own atmosphere. You have to add the 14.7 PSI, which is 1 Atmosphere.

[JeffGST]

Originally Posted by pj91gsx

I got it. thanks for all of the help. you guys are all such a big help. Thanks.

EDIT: is the boost gauge more accurate than the "boost estimate" from the stock MAF or GM MAF? The "boost estimate" does come from the MAS or GM MAF right?

Man, are you getting an education or what, just in this thread alone!!

[My1GLaser]

Originally Posted by JeffGST

Except for the fact that the calculation was wrong.

BoostEst = 20 PSI
Actual Boost = 17 PSI

That is an -8.65% overestimation of airflow.
((Actual Boost + 14.7 PSI) / (BoostEst + 14.7 PSI)) - 1.0


((17+14.7)/(20+14.7)) - 1.0 = -8.65%

He forgot that planet Earth has it's own atmosphere. You have to add the 14.7 PSI, which is 1 Atmosphere.

Yeah thanks man. I had been drinking. I wondered why that calculation seemed so simple compared to when I had to calib my GM MAS last year.

[pj91gsx]

Originally Posted by JeffGST

Man, are you getting an education or what, just in this thread alone!!

Yea, I must know more!
My1gLaser, why did you switch from gm MAF to 2g MAF?

[My1GLaser]

The main reason was because I was breaking in a new motor. I didn't want to complicate my breakin procedure by trying to calibrate a GM MAS. My laptop was smashed in my accident and I didn't have any previous tune to run from. I was already dealing with a much different motor than my first one. I have 272 cams, +1 valves, 9:1 pistons. I didn't know how the car was going to react at the beginning, so I just pulled 4* timing, 5% global fuel and about 10% fuel from the rpm sliders. I was running about 12:1 AFR on pump, but only at 10 psi so it was safe enough. I didn't want to wash down the cyl walls with fuel during the critical first miles on the new motor. And there was no way I was doing repeated 3rd gear pulls to dial in the GM MAS.

Now the motor is broke in, the GM MAS is going back on in a few weeks. I am changing turbos too, so I will probably run the 2G MAS for a week and get some decent logs saved to compare to when I hook up the GM MAS. Idle, cruise, WOT pulls. It will make the calibration much easier if I know what values I should expect when the GM MAS is counting airflow.

[Black_Bullet]

Originally Posted by My1GLaser

The main reason was because I was breaking in a new motor. I didn't want to complicate my breakin procedure by trying to calibrate a GM MAS. My laptop was smashed in my accident and I didn't have any previous tune to run from. I was already dealing with a much different motor than my first one. I have 272 cams, +1 valves, 9:1 pistons. I didn't know how the car was going to react at the beginning, so I just pulled 4* timing, 5% global fuel and about 10% fuel from the rpm sliders. I was running about 12:1 AFR on pump, but only at 10 psi so it was safe enough. I didn't want to wash down the cyl walls with fuel during the critical first miles on the new motor. And there was no way I was doing repeated 3rd gear pulls to dial in the GM MAS.

Now the motor is broke in, the GM MAS is going back on in a few weeks. I am changing turbos too, so I will probably run the 2G MAS for a week and get some decent logs saved to compare to when I hook up the GM MAS. Idle, cruise, WOT pulls. It will make the calibration much easier if I know what values I should expect when the GM MAS is counting airflow.

Do you "feel" any air flow restriction from taking off the GM MAFT and going back 2g?
And how hard is it to dial in the maft, i thought you just plug and play and continue tuning with dsmlink and zero'ing out your maft ? Is it that finicky.

[My1GLaser]

Originally Posted by Black_Bullet

Do you "feel" any air flow restriction from taking off the GM MAFT and going back 2g?

I don't know. The GM MAS was on my first car last April. I wrecked it in May and just got this one on the road this Feb and the setup is totally different with the cams and pistons.

And how hard is it to dial in the maft, i thought you just plug and play and continue tuning with dsmlink and zero'ing out your maft ? Is it that finicky.

Have you been to jeffgst.com? Basically you plug and play, but it will probably run like sh_t and break up bad until you calibrate it. This procedure is spelled out very well on Jeff's site.

As far as it being finicky. Mine was a little bitchy because my 14b was putting oil into my intercooler, which I didn't find out until I disassembled the wrecked car. That will screw with your tune and I didn't have a wideband back then, so I didn't know what the hell was going on. The little wires in the GM MAS that send airflow data to the ECU have voltage going thru them. ANY moisture on those wires will change the resistance across the wire and thereby change the airflow count. I didn't feel like taking the chance with my calibration skills on my brand new motor. Even if the oil was to blame.

Guess what my first purchase was for this rebuild?

BTW, GM cars have a setting in their stock ECU that heats the wires in the MAS up to an extreme temp to burn off any deposits every time you shut the car off. We do not have that feature, so they can be a little finicky in very humid climates (where I live) or on rainy days where the temps can create condensation in your FMIC.

[pj91gsx]

Guess what my first purchase was for this rebuild?

wideband. the quote didn't work, oh well. Does the math equation change from different regions? actual boost+ 14.7/boost est+1.47=-1.

[JeffGST]

Originally Posted by pj91gsx

Guess what my first purchase was for this rebuild?

wideband. the quote didn't work, oh well. Does the math equation change from different regions? actual boost+ 14.7/boost est+1.47=-1.

No changes to the equation. BoostEst takes into account your current elevation when you input it in the DSMlink "Props" menu.

It's NOT what you wrote... actual boost+ 14.7/boost est+1.47=-1.

It is this...
((Actual PSI + 14.7 PSI)) / (BoostEst PSI + 14.7 PSI)) - 1 = Calibration at that specific airflow.