Mr Cowl Hood

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by NoGo:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by LS1derfull:
<strong> ON A HEADS/CAM car with good flow and a cam with 6800 rpm potential, dont underestimate the need to lessen pressure drop thru stock maf sensor as a way of making more power. These motors are healthy and they need all intake tract restrictions removed to make best power. I no this is off topic here slightly but i think its worth making adjustments to fueling to run modified maf.People who believe in hi velocity in intake tract are missing the boat, on this end of system anyway. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">On the very high horsepower applications removing the MAF is the best route.

For most power levels that you see on the street, modifying the MAF is going to do nothing but cause headaches.

If you are cranking out 500 HP on a solid roller, then, yes, I would be the first one to workover the MAF. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Similarly, when I tuned a low compression, 422 ci vette recently, I saw >500 hp with the stock MAF and air bridge (surprisingly), and did no tuning to the MAF table. It idles, drives as a daily driver and AFR's are all in spec, mostly due to a wide band on a dyno. Just my $0.02. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

Good discussion, guys!

NoGo

iTrader: (2)

When you start going to the monster cams and big cubes intake reversion begins to become a problem in the lower RPM. This is just one of the many headaches of the MAF system.
Additionally, you start topping out the MAF at about 580 to 600 HP.
These are just a couple reasons why to get rid of it, but for the most part there is no reason to mess with it.

I totally agree Mr. Cowl Hood (I hate using internet names, it feels like I am in the middle of a Dr. Seuss book). On most applications, there really is no need to seriously mess with the MAF. The stock system works plenty fine for 99% of the people out there.
And for those people who want a 500+ HP very streetable car I think leaving the stock MAF on is a must.

NoGo

iTrader: (2)

Ugh <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" />

I don't want to ***** this guys thread, but you MAF folks are killing me.

Where do LTrims come from? They don't come from the MAF, they come from the OXYGEN SENSORS. And what are the oxygen sensors doing to the engine, they are making a FUELING ADJUSTMENT. They aren't making an air adjustment. When the O2's read +15 Ltrims your car doesn't close up the throttle more to bring the mixture back into spec. It is reducing the injector pulswidths.

O2 sensors are not dead on accurate. If you don't believe me, slap a set of headers on your car and tell me whether or not the O2 readings have changed. Correcting the MAF for what the O2 sensors are percieving is rediculous.

Yes, the MAF is not dead accurate either, but making a correction to something that also controls shift points, timing, load calculations, etc... is going to yield side effects. When you make changes to the injector flow tables THERE ARE NO SIDE EFFECTS. It is a direct adjustment to the fueling, which is exactly what the O2 sensors are doing.

The Dragon: LEAVE YOUR CAR ALONE. YOUR LTERMS ARE FINE. Check your LTerms in 2 weeks and tell me how they look. I guarantee they won't be the same.

I spent over a month logging data from my car every morning on my way to work when trying to calculate an injector offset curve for some SVO 30's. Anybody who looks at the data will easily see that LTerms change from day to day.

Setting your LTrims from +5 to -2 is going to do NOTHING for your car.

Good Luck,
Kevin

Doc99SShome

NoGo,

You DO NOT understand what we are talking about here!

LTFTs come from alot more than just the O2 sensors, By the statement you gave, you have demonstrated that you are out in left field on this issue.

Just for people like you, I ran a test. I got out my ATAP and logged several files as I drove around and sitting at idle in my driveway. The engine has a GMAF as part of the induction system.

Then I swapped out the GMAF for a ported factory MAF and logged some more files.

Lets just concentrate on the idle files. Now at idle, the engine RPM is 860 +- 15. Whether if the GAMF or the ported MAF is installed, you got to accept the fact that the SAME AMOUNT OF AIR IS ENTERING THE ENGINE. But what happened to the LTFTs?

Well, with the GMAF @ idle (Fuel cell 19), the LTFT value is -0.8%. With the ported MAF installed (and after a learned process) the LTFT was +13.3%. The O2 sensor was not changed, nor was any other part. Even the atmospheric conditions were the same. The fuel system is the same, its still factory stock.

So what caused the LTFT value to be -0.8% in the case of the GMAF and why is the LTFT +13.3% with the ported MAF???????

I will leave the rest of this up to your deductive reasoning. Try to impress me.

NoGo

iTrader: (2)

Lets look at your test.

Exhibit 1: Granetelli MAF. Purposefully detuned ~10% to admit more unmetered air to the engine so as to bring a stock cars a/f, normally 11.9, to the peak power of 12.8. The GMAF is inaccurate.

Exhibit 2: Ported MAF. Your kidding me right? A ported MAF is ported SO AS TO ADMIT MORE UNMETERED AIR TO THE ENGINE SO AS TO BRING A STOCK CARS A/F, NORMALLY 11.9, TO THE PEAK POWER OF 12.8. THE PORTED MAF IS INNACCURATE

What where you trying to prove with your test? That showing the engine less air will move the LTerms around? We know that already.

Now do a test that will prove my point. Take your stock MAF put it on the car. Do a WOT run. Tell me what your timing is (98 to 00 should be 28, 01 to 02 should be 19-22).
Now put the GMAF on the car. Do a WOT run. Tell what your timing is. I bet it is in the 30's.

Yes, swapping the MAF's have adjusted the LTerms, but you just inadvertantly adjusted your timing, shift points, and engine load calculations with your LTerms adjustment.

Why mess with every calculation in the engine when adjusting fueling, when you can adjust fueling directly with no side effects?

The Dragon

iTrader: (6)

I am floored by all the information in this post <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

I can't thank all of you enough for the assistance.

I'm gonna be studying for a while <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

BTW: gonna get the stock MAF off of the WS6 tomorrow <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

Bink

Very Interesting!!! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> <img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" /> <img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" /> <img border="0" alt="[driving]" title="" src="graemlins/gr_driving3.gif" /> <img border="0" alt="[driving]" title="" src="graemlins/gr_driving3.gif" />

Doc99SShome

Nogo,

I am sorry that I upset you about this issue. But you were the first to bring up the disservice business. So I apologize to you for my comment.

There are a few fine points about re-calibrating the MAF table: Because the MAF table (MAF frequency vs incoming mass air flow) is a non-linear relationship, one can not correct the LTFTs by making a simple across the table multiplication. If this is what tuners have done in the past and it did not work out, I can see why they have gone to changing the fuel table.
In my case (if I remember correctly), the top end of the MAF table was increased by 4%, the mid-region by 7 or 8%, and the idle area changed 15%. In between these areas, one must slowly blend in a smooth transition. Always check your work with the graphics viewing options. Tuning the MAF table takes alot of time and several runs on the street, so I can understand why tuners do not re-calibrate the MAF table, it simply takes to long and can not be done with one simply multiplication. So tuners must defend their approach, even though, they must know that the MAF table does not represent the flow characteristics of the MAF in use.

Also, there is no such thing as "un-metered air" inside our MAF sensors. What is actually happening is two different MAF sensors will output different frequencies while measuring the same mass air flow rate. It is the job of the MAF table to calibrate each type of MAF to its unique rsponse signature. A vacuum leak is "un-metered air", do not confused this with how a GMAF or Pace MAF is measuring air. MAF sensors do NOT measure mass air flow directly, the measurement is indirect, that is why we have a translation table (MAF table) to convert frequency or voltage or counts to mass air flow.

So, all in all, from the above statements from Tim and Nogo, if the stock MAF sensor with screens can support over 500HP, everybody with a bolt-on only car (including heads/cam cars) should keep & use the stock factory MAF sensor. Only those people with superchargers or turbos might need an aftermarket MAF. Is this a fair statement?????

NoGo

iTrader: (2)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Doc99SShome:
<strong> Nogo,

I am sorry that I upset you about this issue. But you were the first to bring up the disservice business. So I apologize to you for my comment.
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">[qb]

No big deal. It's the internet. It's all in fun anyways. No offense taken, and I hope you are not offended by my comments.

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">[qb]
There are a few fine points about re-calibrating the MAF table: Because the MAF table (MAF frequency vs incoming mass air flow) is a non-linear relationship, one can not correct the LTFTs by making a simple across the table multiplication.
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"></strong>

Yes you are correct. The MAF cannot be applied linearly for the most accurate results. I will admit most can get away with slight block adjustments to the MAF though, it doesn't hurt. My MAF curve on my personal car is shifted 4% up. The problem is that suggesting someone mess with their MAF table on the internet leads to people thinking that any MAF adjustment is okay. I have recieved several emails of discouraged people wonding why their 25% adjustment to their MAF curve killed the car / transmission / times although their LTerms are dead on.
It isn't a matter of what is right and wrong, it is a matter of beginner tuners misconscrewing what we post here.

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif"><strong>
If this is what tuners have done in the past and it did not work out, I can see why they have gone to changing the fuel table.
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"></strong>

Most tuners already know that the MAF curve is not linear, and if they don't, it only takes one customer with a VERY ported MAF to put them on the learning curve. Both methods work to adjust LTerms, but the fuel tables are just quicker and simpler. Plus there are no side effects, which is why I suggest it.

<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">
Tuning the MAF table takes alot of time and several runs on the street, so I can understand why tuners do not re-calibrate the MAF table, it simply takes to long and can not be done with one simply multiplication. So tuners must defend their approach, even though, they must know that the MAF table does not represent the flow characteristics of the MAF in use.
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Tim Sloper was actually nice enough to put a very important equation up which greatly simplifies recalibrating an MAF. With this eq it only takes a couple runs on the dyno to plug in a proper transfer curve.

<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">
Also, there is no such thing as "un-metered air" inside our MAF sensors. What is actually happening is two different MAF sensors will output different frequencies while measuring the same mass air flow rate. It is the job of the MAF table to calibrate each type of MAF to its unique rsponse signature. A vacuum leak is "un-metered air", do not confused this with how a GMAF or Pace MAF is measuring air. MAF sensors do NOT measure mass air flow directly, the measurement is indirect, that is why we have a translation table (MAF table) to convert frequency or voltage or counts to mass air flow.
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I am going to have to disagree here. But rather than write a book, I am going to say we agree to disagree.

<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">
So, all in all, from the above statements from Tim and Nogo, if the stock MAF sensor with screens can support over 500HP, everybody with a bolt-on only car (including heads/cam cars) should keep & use the stock factory MAF sensor. Only those people with superchargers or turbos might need an aftermarket MAF. Is this a fair statement????? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Yes. Unless you know what you are doing and what messing with the MAF is going to do, I wouldn't mess with the factory MAF system.

There really isn't an aftermarket MAF (yet) that extends the upper bounds of the current MAF enough to make it worthwhile to the FI guys. Most goober with PE tables and such to increase fueling or some just bail on the PCM and go speed density.

Anyhoo, I am just one tuner. Everybody does it different and has their own oppinions.

Good Luck,
Kevin

Doc99SShome

Kevin,

No problem here either.

It is interesting to note that I have never seen a frequency from my MAF above 10250Hz (this use like 6,500RPM WOT with a stock displacement motor), while the MAF table goes up to 12000Hz.

There appears to be room on the top end that I can not reach and dont need with my motor.

NicD

iTrader: (7)

I would never screw with the MAF table. Use injector constants instead.

NoGo

iTrader: (2)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Doc99SShome:
<strong> Kevin,

No problem here either.

It is interesting to note that I have never seen a frequency from my MAF above 10250Hz (this use like 6,500RPM WOT with a stock displacement motor), while the MAF table goes up to 12000Hz.

There appears to be room on the top end that I can not reach and dont need with my motor. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">At 375 HP (just guessing from your MAF freq), you have room to grow (like most of us). Thank god GM sized most of their important electronics at ~80%.
Maxing out the MAF takes around 580 RWHP.

Doc99SShome

I pulled 400.3RWHP @ 6200-6300RPM on a DynoJet chassis dyno.

My car is an MMS stage 2x head/218 cam car with full intake/exhaust mods and 4.10 rear gears. I take pride in the fact that I do all my wrenching myself along with the PCM tuning. My experience is limited to only my car, so your experience must far exceed mine. All my comments in the above posts mainly come from my personal experience which included sitting in my car while it was dyno tuned by my friend Steve.

About the person or persons who might have made a 25% change to the MAF table: no wonder they have issues!!!!!!

LS1derfull

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by NoGo:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Doc99SShome:
<strong> Kevin,

No problem here either.

It is interesting to note that I have never seen a frequency from my MAF above 10250Hz (this use like 6,500RPM WOT with a stock displacement motor), while the MAF table goes up to 12000Hz.

There appears to be room on the top end that I can not reach and dont need with my motor. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">At 375 HP (just guessing from your MAF freq), you have room to grow (like most of us). Thank god GM sized most of their important electronics at ~80%.
Maxing out the MAF takes around 580 RWHP. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Are you basing this 580 rwhp on max airflow of stock maf? If so than what does it flow, because there are formulas for max power at certain flow levels. Do you know?

Colonel

No, I think he's baseing that on the fact that the MAF will only report (or maybe the PCM will only acknowledge) but so much airflow...seems like it's like 45 or 54 lbs/hr, I forget. Anyway, you get the idea.

With a stock MAF the limit works out to be somewhere in the neighborhood of 580 RWHP depending on other factors (drivetrain efficiency being one of them.)

LS1derfull

Thanks steve, i understand, but just for kicks i flow tested stock screened maf, at 20" of water very close to Carburetor 4 barrel test standard it flowed 820cfm, with no air lid. Had i tested with lid it may have flowed more. This is enough flow with medium sized cam to not be a restriction to hp at reasonable rpm. So i may throw stocker back on mine for LS1edit tuning. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

ChrisV 02 - Z28

iTrader: (1)

AS to not beat the subject...

To recalibrate the STOCK MAF (which have ported end) would I just do some partial throttle runs all the way through the RPM range and based off the recorder MAF frequency, would i adjust that corresponding air flow(g/s) only, in order to adjust that moment in times LTFT up/down.

So if for example at some point in time my maf frequency is X and my LTFT are say +10% would i scale that indivdual cell (X) on the maf table by 110% to recieve a new calculated value for that frequency only. do that for say every maf frequency say in 100(hz) steps or equiv, and layout those new points on a graph. Then do a curve regression to best fit a smooth curve through thes new calculated points.

From this new smooth regressed curve update each cell in the MAF table to the new value.

IS this correct? I know is it a lot of work, but is is the right way to do it with running ported maf ends? <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

pkincy

iTrader: (1)

OK, let me make some basic assumptions as a base line. My block learns (ltfts to you OBD2 folks) are 4% rich at idle (with cam so only slightly low load) go lean -2% at low load mid rpm, are spot on at higher rpms and low load (cruise) and lean high load all rpm. The last is wot and that certainly would have us going to the PE tables.

What would you guys do for the driveability issues. All the non wot throttle issues above. You certainly wouldn't change the inj constant as you can't hardly move it in two directions.

In my opinion you have to go to the MAF (and backup this by fixing the speed density tables and that is a thread all in itself) to get anywhere. Or is there another table in the LS1 edit where I can modify resultant block learns on a load/rpm specific basis??

Perry

Doc99SShome

Chris,

Basically, what you said is the way I went about it (modifing the MAF table based on the LTFT values). However, I did 1/2 of the change on my first change. Your example of 110% (LTFT +10%), I would multiply by 105%, and then go out allow the PCM to learn, then take more scans. BUT, you can not make one multiplication thru the entire MAF table and think that you got it right, because you do not!

Concerning the scans: I try to visit as many fuel cells as possible. One type of scanning I conduct is to get on an Xway, short shift each gear up to 4th (I have an M6 car), then while I'm in 4th at a very low speed slowly accelerate, take the car speed up to what is responsible under your condition, staying in 4th gear. (For an A4 car, I would put the tranny in Drive, not overdrive.)

I also take scans at several steady state conditions, the first is idle (when I return from the street scanning session) and others at like 25mph, 45mpg, 65mph (whatever)

Now I got the scans for analysis. I do record MAF frequency, Engine RPM, LTFT, never STLT, fuel cell #, timing,,,,.

After analyzing the scans, I locate the different portions of the MAF table for changes. Typically, I break the table down into the idle and just off idle region (1500-3000Hz), mid-range region (5000-7000Hz), and upper end region (8000Hz and above).
Note that there are gaps. I average the LTFTs for these respective regions and multiply by 1/2 of the LTFT avg value for that region. (I use 1/2 the value because I do not want to make to big of a change at a time and cause other problems. So if the LTFT value is +15%, I would multiply by 107.5% for that region.) In the gap areas of the MAF table, I prorate the change to the flow rate so that I maintain a smooth looking curve. The MAF table is a non-linear curve which gets more steep at higher frequencies. Always check your work in the graphics mode in LS1Edit and make your changes to a new file name so that if you have to you can always go back to the original MAF table values. Also, if you saved the stock PCM stuff, and left it as is, their is a compare file option in LS1Edit which is nice.

The objective is to get all of the LTFT values between 0% and -5%. The -5% is a little arbitary.
If you re-calibrate the MAF table for a ported MAF sensor, it will take many scan/LS1Edit cycles. If you get it done properly in 5 cycles, you are doing great, IMHO. I took about 8 to 10 cycles mainly because this was my first tune.

In some post, a tuner (who does nor like this method) stated that an LS1Edit user changed the entire MAF table by 120% and then had drivibility problems. Well, DAH, no wonder, 120% is too much. With my ported MAF installed, I scanned LTFTs at 18% up to 22%. In order to re-calibrate the MAF table, no cell was changed more than 15%. So I conclude that the change to the MAF table and the LTFTs are not a one to one correlation.

Doc99SShome

Perry,

You are very close to 0% for LTFTs, in fact, it goes both + and -.

What drivibility issues are you talking about?

And, what is the LTFT at WOT???
If your LTFT is 0% at WOT, you do not need to do anything about the LTFTs. You are good to go.

If you are looking for more top end power, then (if you have LS1Edit) work on the PE vs RPM table and the main timing table.