mikeyc6

After losing torque on the low end after installing a Donaldson intake and GMS MAF, I decided to pull the GMS MAF and put the stock MAF (with no screen) back on. The results are very interesting! As with all the tests, I drove the car for a while at part throttle with a few WOT bursts before testing. Weather and other conditions were very close to the same for all runs and any small changes in weather conditions like humidity, temp, barometer were accounted for anyway. Here are some things that I noticed and some preliminary conclusions I made:

(1) On the run with just the K&N filter, stock air box, and no MAF screen, there was a dip in the curve at about 4800 RPM. It is possible that this was caused by turbulence in the air flow at that RPM range, causing the MAF to get confused... or maybe dirty MAF wires (more on that later).

(2) The Donaldson intake definitely flows more air over about 5000 RPM. You can see that the torque curve is significantly higher there. It seems to do nothing below that range, only showing an improvement in the high RPMs. Fine by me, and it makes sense that this is what we see. My conclusion here is that the stock air box is a significant restriction, but only above about 5000 RPM.

(3) The GMS MAF had caused a significant loss in torque below about 4500 RPM or so. I did two tests with this configuration just to make sure I was getting accurate results. The run posted above with the GMS MAF was actually the *better* of the two runs, but they were both within a couple lb/ft in any case.

(4) The run with the stock MAF was with the exact same configuration as with the GMS MAF (both had the Donaldson intake installed). Before reinstalling the stock MAF though, I cleaned the tiny sensor wires with a moist Q-tip (I used water because I didn't know if alcohol would cause a reaction with the wires/elements). As you can see by the graph, not only is my 4800 RPM dip not there any more, but I am now back to where I'm making good low end torque AND getting the benefit in the high end as well. I don't know whether that initial dip in the K&N/stock run was due to the stock air box causing more turbulence (and the Donaldson's shape/configuration causing *less* turbulence) or whether me cleaning the MAF wires helped! Either way, the dip is gone, or at least much less pronounced than before.

Any way you look at it, it appears that the stock MAF works much better for me than the GMS unit. Does anyone know whether the GMS MAF is returnable? I've only had it for a few days. If not, it's money wasted because it really kills the low end... at least for me. Given the results of my testing, there's only two places I'd consider putting the GMS MAF: on the shelf in the garage or back with Mr. Granatelli. ;)

Mike


[Modified by mchaney, 10:48 AM 8/10/2001]


[Modified by mchaney, 10:49 AM 8/10/2001]

NetJunkie

Do you have the normal GMS MAF or the one that is 5% rich?

mikeyc6

I have the normal GMS MAF, not the 5% rich one. Didn't see why I would need a 5% rich MAF when I have no other mods other than the Donaldson intake. If they are selling MAFs for C5 Corvettes with little to no mods, why would they sell you a MAF that they know is going to run lean? If they are doing that, I think they should change the "default" one up to 5% rich if that's what is causing the problem. It was my understanding when I bought it that you should get the normal one if you have no mods or just an intake mod. Based on what I've seen with these tests, it looks to me like they shouldn't be selling the "normal" one at all! That is, if the 5% rich version gets rid of the low end torque problem.

Mike

chuckster

You know I wish I had a dollar for everytime this comes up.

Of course the car runs better with the stock MAF and Screen.
That's the WAY IT WAS DESIGNED. You did not GAIN a thing. All you did was make it run the way it was supposed to at the factory.

If you ran an Autotap log you'd see the problems clear as day. They can be corrected with a MAFT.

Making changes to your engine and not monitoring the results (i.e. Autotap, Easesim) You are shooting with a blindfold on.

When you increase airflow and start messing with the intake and MAF ends you MUST HELP the PCM. There is only so much the PCM can do on it's own. You have to monitor and reprogram with a MAFT Period.

Remember, everyones car is different, they are in different parts of the country, different temps, gas, driver types, humidity, Altitude etc.....
You MUST tune to your car. That's why 0% and 5% Granatelli's only work sometimes. It would be like setting my home computer up like my buddys at work. Both Compaq's but different.

Bottom Line...If you tuned with a MAFT you would have left Rubber on that Dyno :cool:

I personally gained more from my MAF ends and MAFT than I did with my Powerloader!
I will dyno soon to prove it.

mikeyc6

Ok. Point well taken, and I intend to get a MAFT and autotap as my next purchase. It doesn't take me long to figure out that if you want it done right, you have to do it yourself.

My problem with the GMS is this: if it doesn't measure airflow properly (for an LS1), then what's it for? The problem with the stock MAF was supposedly when you remove the screen, it can't properly measure airflow any more because it was designed to have the screen in place. The GMS MAF is touted as a "fix" to this because the electronics have (supposedly) been calibrated to account for there being no screen, no airfoil to split the air, etc. It is advertised to produce a 10-15 hp gain *because* it is supposed to be designed so that it measures air properly and transmits the proper signal to the LS1's engine computer.

In theory, if someone took their MAFT and figured out what parameters were needed to produce more power on a stock (or near stock) engine and just put those parameters into an aftermarket MAF (like the GMS), it should work. At least, I don't think there's any reason for it to kill your low end torque by 15-20 lb/ft from 2000 all the way up to 4500 RPM. In a couple of the descriptions in the mall, it describes the same MAF as being used on different engines (like the vortec V-6 for example). If this is a "generic" MAF designed for multiple GM applications, no wonder it doesn't work!

If the GMS doesn't work or is inappropriate for the C5, then I don't think it should be sold in the mall. Or if it is designed to work with specific other mods, those mods should be listed. There are probably a lot of other people like me who don't have the time to spend days/weeks tweaking a MAFT and mulling over autotap data and will think that the GMS MAF is a reasonably quick answer to getting the fuel mixture right because that's the way it is presented. They may also be a little leary of the MAFT as I was (and still am) regarding it dropping a signal at higher RPM due to noise and creating huge power dropouts. There are some pages on the web regarding how to open the MAFT up and solder capacitors onto the circuit board to prevent this. Doesn't give you a very warm feeling.

All of those factors went into why I decided to try the GMS MAF instead of going the longer route. Of course, all good things come in time... if you don't have time to do it right, don't do it... etc. etc. I have no problem taking the time to do things right but I also do have other things to do, so I saw no need to reinvent the wheel if someone had already found a way to make a truly accurate MAF. Apparently that's not the case. If you have a MAF that truly measures the correct amount of air going through it and sends the appropriate signal, the PCM should be able to figure out what mixture to use. The "normal" MAF should be based on no mods after the MAF unit. Forward of the MAF unit, stuff like filter boxes, ram air, etc. should be fine. The only time you'd need to change the signal is when you change/mod something *after* the MAF because if you do that, you could potentially change the ratio between the amount of air that passes the MAF wires and the amount of air that actually gets *used* by the engine, for example, if you do a bigger TB, different rockers with different lift, etc. Wouldn't that make sense to you? In the latter case, you could tell whoever builds the MAF what mods you've done and the MAF could be tuned for your mods. If you have no mods after the MAF itself, the "normal" MAF should be used because it is based on proper airflow for a stock setup. Wouldn't that make the most sense? I thought that's what I was buying...

Mike

C5TECH

On my 2001 the stock MAF without screen is superior to the GMS. I believe the airfoil is important for proper operation. GM has admitted the screen is not needed if you have a straight intake.

TAL

Did you guys read my post?
http://www.corvetteforum.cc:88/zerothread?id=130680

I had the Granetelli MAF and felt I lost TQ...this post confirms this. Even on the side of the box it tells you it makes power 3000rpm & up.

But what about 3000rpm & BELOW??? I think you lose power! TQ is the most important thing on a street driven vehicle (IMHO of course!).

Try the JPS velocity ported MAF. I think it really works.


[Modified by TAL, 3:30 PM 8/10/2001]

chuckster

I'm Glad you see light :cool:

The MAFT problems of the past are fixed. Mine is 1 month old and is great.
GMS I agree should not be sold. There is about a 50/50 decision on it's effectiveness

I'll venture to say....MAFT and AutoTAP with MAF ends has a 100% aggreement on effectiveness :cheers:

mikeyc6

I'm wondering if the stock MAF without the screen might not work better if it was installed just before the throttle body opening? As it is on a stock system, the MAF is right at the mouth of the air box where the air hasn't had a chance to straighten out. I believe a short, smooth, pipe-like spacer could be made to sit where the MAF normally sits (down by the air box). You could make a second piece that replaces the accordion/rubber piece up by the mouth of the throttle body. This could be a smooth molded (short) piece that attaches to the stock intake and accepts the MAF here. On the other side of the MAF would be a (also short) piece that attaches the MAF to the throttle body opening. The whole point of these three small plastic pieces would be a kit that relocates the stock MAF on a stock intake so that the MAF is farther downstream and in the flow of straighter air, thereby allowing removal of the MAF screen on a stock MAF by putting the MAF in a straighter flow of air. As a side benefit, you could get rid of that little accordion piece up by the throttle body. Replacing that with a smooth plastic piece might provide better flow via less turbulence.

With the MAF right at the air box opening, I'm afraid the air doesn't have a chance to straighten out before passing through the MAF. Do you think such a product would be of use? Would people be interested in this if it was proven to work? If we try it and it proves positive on the dyno, I believe we could market it at a very reasonable price since it's just three plastic pieces and maybe some gaskets.

Mike

ToplessTexan

Amen! I tried to pin Granatelli down on this point at LS1.com in his annual MAF 101 thread earlier this summer without much success. All I wanted was his definition of the term calibration and I didn't get it. The meter has either (a) been calibrated to accurately report the amount of airflow or (b) been calibrated to (over-) under-report the amount of airflow. An "accurate" meter would have no value beyond simply being able to flow more air.

Which is exactly how the GMS sensor is designed. (Well, maybe not using a MAFT but the analogy is sound.) It's sort of MAF sensor and (non-adjustable) MAFT all rolled up into one. One topic that came up was a tuneable GMS MAF sensor. The price floated was outrageous given what it was. :rolleyes:

Some folks are really happy with theirs. I agree with the anti-snake-oil sentiment, violently :D, but think that consumers have some responsibility in investigating the products they buy. (And I appreciate that you've done a good bit in this case, stopping just short of comparing how the GMS works to the other potential solutions you identified. It always seems to be that last step...) That's why your post with quantified results is so important and valuable. The kind of discussion you can now have is substantially improved over the SOTP advocacy that you often see. That's at best useless, regardless of how well intended it is.

Hang in there. It's easy to spend money and not get the results you want. Eating the cost of the GMS is cheap in the grand scheme of things. :D

Also, I don't believe that larger ends + MAFT is the only game in town. ;)

As to the question of piping, you are addressing many of the issues that led Jim Hall to design the TRIC as he did. Have you looked at the Sidewinder (the latest incarnation of the old two piece TRIC)?

EasyGoin

Good post Topless. I feel the same way about the powerloader. "Best bang for the buck"--"Get it and just hold on" Then you hear dyno reports of just 4 HP. Hold on for 4 HP?????. As John Stossel would say "GIVE ME A BREAK"
Ed Wright can do the same thing with a lot less aggravation. BTW Read this.

"I have some MAF experiences on Ed Wright's dyno and have done substantial research on this. This is what I've learned and seen.
Ported MAF, MAF ends are not good for your car. They you say, well tune it. I say you can't. Been there, done that. ON Ed's dyno.
(that way i eliminate the flame as being a jeep tuner )

erratic A/F mixtures from bout 4200 up, loss in smootheness to both HP and TQ, constante computer feedback to fuel injectors, wide/tight, wide/tight. Even with fuel MAP re-done (LT1), it still did it. Put OEM MAF back on, re-loaded the last correct tuning (we had it tuned then he wanted to experiment) and it was all good to go again--smooth and power back up to 441/436 (dyno sheet on the link in my sig)

I've seen auto tap data from the Pace MAF WITH LS1 ELECTRONICS. If i was going to buy one (and I might, AND keep my OEM piece), I'd buy this one. not just a larger one like some other companies sell.

From what I've seen AND heard, proting the MAF and/or using MAF ends is way ghetto. doing it without custom tuning and/or an A/F measurement is closer to stupid.

I don't believe in the GMAF either--check out what Steve Cole had to say about it (do a search on this forum)

I'm glad I haven't fallen into the trap of MAF modifications, particurally doing it with no way to analyze data.

You're asking for troubles if you do it, maybe not immediately, but the PCM will figure it out and in the end, you'll have problems. I've seen it, heard about it, listened to people up in arms over it.

In short, the pace MAF SEEMS to work. the OEM MAF works. The rest is, IMHO, trouble brewing.

Hope I've helped. Make sure to do some research before you spend you hard earned money on stuff that is going to make you have to spend more and probably not give you what you wanted.

Chris
Concerned MAF dude.

------------------
'02 Arctic White/Ebony 1LE M6 Firehawk Trans-Am !TCS, !changer, and !Hurst, VIN assigned 7 Aug. Auburn diff and all the pretty stuff. Pro 5.0, MTI clear lid/Holley Powershot, and FTRA waiting to go in. Former car: 1997 Z28 396 with 441/437 RWHP/TQ totaled 6-08-01. Currently:
2001 CBR 600 F4i--D&D slip on
1991 Nissan Pickup--CBR Hauler, daily driver
aka: Chris' 396 Z @ z28.com http://www.sa-fbody.org

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PK red98TA
Veteran
Posts: 2622
From: Plano, TX
Registered: Jul 99
posted August 09, 2001 08:46 PM


Above is a quote from LS1 that I found interesting

See Ya :seeya
Easy


[Modified by EasyGoin, 9:46 PM 8/10/2001]

Lashtal

Do you think that a GMAF at +5% rich would make a difference?

Interestingly enough I have a Stock MAF with the screen removed combined with the Halltech Magic Box. Seems to work really well. No more codes after putting the MB on (the codes read "lean").

I'm planning on going with Stage II or III Heads and a hotter cam soon. I wonder if a stock MAF will work properly - or if I need a GMAF +5% or +10%???

Ideas or real like experiance anyone???

Chuck Broten

All of this talk has caused me to think about how the MAF functions. I agree with several comments that say the MAF should measure true air flow automatically. In other words, if you install a larger filter and cobra head that flows better the MAF should accurately convey the information to the computer. Why doesn't this seem to be the case?

I think that GM knows exactly how much air the MAF will see from minimum to maximum operation. They also have to add in temperature variations (I think). They then design the electronics so that the cooling of the elements in the MAF fit the expected air flow range and send the appropriate signal to the computer. I suspect that the sensor is nothing more than resistance that changes as air flow increases and decreases causing the signal output to change. The translators simply take this signal and add or subtract from it to fool the computer. I also suspect that the sensor wires have upper and lower limits preventing them from measuring extra air.

Adding a recalibrated MAF accomplishes the same thing as a translator except that it is fixed.

I have thought about adding a new MAF or translator but agree with the statements about being able to see the results with something like Autotap... etc.

I saw a post where someone put a fixed resistance across the temperature sensor wires and had good results. This would set a flat baseline for temperature and the MAF would then only have a single variable (if in fact the temperature is used in the MAF) to use when modifying the signal. I suspect that a wide range of temperature variation would make this mod troublesome.

NOTE: All of this is just me thinking because I don't have any technical literature to really check things out. If anyone knows where I can find this type of information I would appreciate it.... because I could be ALL WET!
:conehead


The problem I have is money. As much as I would like to do all this, mainly because it is fun, my better half is beginning to look at me sideways when she gets the Visa bills..... most of them from LAPD and Shawn... :cheers:

mikeyc6

I've thought of that myself. I would think that the computer would have to combine data from the MAT (air temp sensor) with that from the MAF to see how much air is entering the engine. Hotter air would have less effect on the cooling of the MAF wires than cold air. If that's the case, you should be able to just add a resistance to the MAT sensor either in parallel (if you want to decrease resistance) or series (to increase resistance). This would fool the computer into thinking there was warmer/colder air entering and may do the same thing as a MAFT in the end, only it would cost about $2.

The only problem with this is:

(1) You don't know what (if any) relationship the PCM makes between MAF and MAT readings and
(2) The resistance of the MAT versus air temp is not linear.

Mike

DUKE

Looking forward to seeing your follow up. Thanks for the info. I am considering the autotap and the maft. Can you explain how you physically go about adjusting the A/F with the maft?

silversport

This is the kind of back and forth conversation that makes this Forum so great!!!
We don't have to agree or we can at least agree to disagree but this information is INVALUABLE to me!
I LOVE this Forum!!! :chevy

DAP

I think one of the vendors here that sells GMS MAF needs to do back to back tests on an '01 LS1 6 spd ('01 b/c the MAF is already bigger, so gains will be minimized-if any).

Test should be conducted with a Vortex airbox (most common) and some type of duct & coupler behind the MAF to get the smoothest, best shot of air into the engine.

Baseline with stock MAF, stock MAF with screen removed, GMS MAF, GMS MAF 5%.

Can somebody please do this with dyno results to back it up?

RPOZ4Z

It looks like I'm going to try and autotap my GMAF and stock MAF to see which one works better on my car. I really haven't had the chance to use autotap much since I got it so.......................
my question is, should I remove the screen on the stock MAF?
and should I give the PCM time to "re-learn" after I swap the MAF?
I may also try the MAT sensor trick.





[Modified by RPOZ4Z, 3:55 PM 8/11/2001]

ToplessTexan

A MAF sensor is an airflow meter, a measuring device, it is not a mechanism for adjusting timing. Any well designed measuring device will not unduly alter the subject being measured. Using MAF ends for timing adjustment is about like using a cescent wrench as hammer :D and does indeed alter the subject being measured. Sure, you can attempt to compensate for this effect, but why when there alternatives? (Please pardon my passion on this topic, the physicist in me is wretching at this point seeing all the misinformation and misunderstanding on the whole MAF thing.)

It fails to do this (to the level of design specification) only when you alter the physical configuration of the MAF assembly.

Keep in mind that this sensor is used in an application that sees low RPMs most of the time. It is designed with that in mind and is most accurate in those ranges. Additionally you see more precision allocated to the various translation tables you mentioned in the lower RPMs. This isn't inconsistent with your understanding of how the MAF works, just a caveat.

Are you thinking of team-zr1's recent post on his IATricker? It is fixed, but adjustable. :D Nice for fine tuning IHMO, but not the best first order solution.



[Modified by ToplessTexan, 6:37 PM 8/11/2001]

C5go

Okay, I have a 2001 as well. Would I benefit from removing the MAF screens as opposed to leaving well enough alone? Would anything else have to be done if I did remove them? And finally, how does one go about actually removing them from the MAF? If it matters, I do have a vortex and power duct installed. Any comments would be appreciated. :confused: