LeftoverChinese

I couldnt have said it better myself sir.

anaik

Did you destroy your screen removing it because there was no retaining ring? I stated earlier in this thread that '96 and '97 had no retaining ring, but some responded that they had one. It appears some OBD11's have one and some not. Just trying to get my data straight.

Brent94Z

Nobody should do this if they feel uncomfortable.

I have/had a 94/95/96 and all of them have the MAF screen removed. None of them required damaging anything either (not sure why some seem to be glued in while others are held in by a c-clip???) to remove the screen. Since I'm at the point in mods where the $$$ per hp ratio is extremely high, I'm all for anything that I can do easily and for FREE... even if it is only 0.5 hp. So, for me, 10 minutes and zero cashola for 0.5 hp is a big thumbs up in my book. And, if I were to have problems, I'd just stick the sucker back in and all I lost was 20 minutes of my life tinkering with my car and I can deal with that

shoebox

Extensive controlled testing would have to be done for me to believe that removing the screen does not have some effect on calibration (you would have to consider all driving conditions and throttle openings). Being that not everyone has the same intake plumbing and such, removing it can have different effects.

Obviously it does affect some people's cars because they have erratic idle or surging. That, IMO, says it has an effect on calibration (whether anyone's particular setup makes it noticeable or not).


94formulabz:

My opinion is that the screen was put just before the sensor (and only there). This allows for a more laminar air flow right at the sensor to allow uniform cooling/accuracy of the sensor (which is how the thing works). Moving the screen to some other location would not have the desired effect.

I'm beginning to regret posting on this thread. :blah:

94formulabz

Edit* Whoops, i didn't type anything yet:

Shoebox, come on it's all in good fun.
I completely agree that it is there to promote laminar flow, and *maybe* to protect the maf if some debris did get in ther. I was trying to make the same point as Brent94z that it's no different then changing your cai and getting more flow, he just made it more eloquently.

IMO it doesn't matter if the flow is turbulent because the turbulent eddies occur in the reference of the flow. Lets say the air is flowign 2 ft per second(pulled out of my ****) through the maf, then the swirls/eddys of the turbulent flow are also moving through at 2 ft per second and the 'snapshot' that the MAF sees is air flow vector with 2ft per second magnitude in the x direction, and vectors in the other directions due to swirling but on an order of magnitude less. Now if you change your frame of reference to move with the flow, then it is very easy to see the swirls.

Typically the pictures of turbulent flow eddys you see are for a viscous dense fluid. A quick check of the reynolds number reveals that although the viscousity of water is 50x greater than that of air. Since this appears on the bottom of Re that means air is 50 times more likely to be turbulent for the same flow conditions. Add in that water is approx 800x the density of water, which appears on the top or Re, and water will flow much more turbulently at the same mean velocity through the same pipe.

NO the maf wasn't designed to flow water!!!!!!!!!!, I'm just trying to make the point that the airflow is not as turbulent as one might think, and even with eddys the individual velocitys are still all in the same direction as the mean velocity, just small angles off.

Maybe people who get rough idle have disturbed something else, like the maf sensor itself, wires, or possible a bad seal on the bellows to maf housing???

Either way, no problems here
-brent

GREGG 97Z

I removed the screen on mine three years ago and ported it at the same time. My screen was held in there with some sort of epoxy glue, there was no clip and I messed the screen up a bit taking it out. I never noticed any difference good or bad with it while the car was mainly stock. I recently picked up a stock maf housing & screen and switched back to stock since I had a high end miss which I thought it may be due to the pcm reprogramming and the modified MAF housing. It didn't fix it but I am sticking with the stock one for now anyway. Just my $.02 on this issue.

MentalCaseOne

: :

No wonder I am going Mental........

MentalCaseOne

I think he forgot the MAF reads Mass of air by temperature differential and not exactly by air velocity. Ad just one eddy in the wrong place and the MAF will read God knows what.


is like someone here who argued with me about 1 volt off while reading the Temp Coolant sensor was not big deal... Only he forgot that one volt at 220* farenheit is only about 30 degrees of temperature and if you are off by one volt when the ambient temp is about 20 degree farenheit (coolant temp when engine cold too) the pcm is reading nearly 90 degrees off! (all readings there are exponential)


Sometimes it may not seem like much but the smallest things can snowball into the largest disasters.


I am with Shoebox. sorry guys, shoot me if you want but I would rather talk to a true GM Injeneer to find out as for why they felt the need to go the extra expense and add that little funny screen in there...


Marvin

CGrant

I have my dyno tune on the 3rd and both speed inc and FLP both said to get a untouched stock MAF for my dyno tune.
There is a reason for this.
They have both been doing dyno tunes for some time now.
I am taking their advise, But to each his own, The only thing that I know is the low rpm stumble that I have been chasing for like a year now is gone with the replacement of my ported maf with a stocker, I was about to replace the opti cause it was the only thing left. I am sure glad I didnt replace it.
Chris...

Injuneer

What you don't appear to understand is exactly how the meter works. It uses the wires to heat the incoming air approx 100degF above its original temperature. It measures the power required to do this, and can then calculate the mass of air that is passing the wires, because it knows the specific heat of the air.

What you need to remember is that the wires only touch, and heat a very tiny SAMPLE of that air. In order to calibrate the meter, it has to be of a fixed diameter, and the calibration needs to reflect the variations in flow velocity across the face of the open area. The screen is there to provide a uniform, repeatable flow velocity distribution. The tiny SAMPLE heated by the wires must reflect the flow across the full cross-sectional area. And it needs to be able to operate over a huge range of flows, from the typical 6-9gps at idle to 220-240gps at max rpm (stock engine). This entails operating in both the laminar and turbulent flow regimes.

The only way the meter can be calibrated it to provide a relatively uniform and repeatble flow velocity distribution. The central "wing" is also there to promote uniform flow, and to prevent the plastic center support from causing additional turbulence and flow distortion. The velocity distribution can be affected by a number of external factors as well, including the configuration of the duct leading to the meter, and the configuration of the duct at the exit of the meter. GM was able to eliminate the "screen" in the LS6 because the inlet ducting is totally symetrical, on both the inlet and outlet sides of the meter. The LS1 is very similar, as is the WS6 setup, meaing the screen has less value in these applications. But the base 4th Gen LT1 has an irregularly shaped, non-symetrical inlet, and a sharp bend on the outlet duct, promoting non-uniform flow velocity across the face of the meter.

If you want to remove it, remove it, but keep it in one piece if you can, because a) you may not like the results, or b) in the future you may go for a "mail-order" tune, and the tuner is going to find it more difficult to do that tune because you have altered the calibration of the meter. The dyno test I saw showed a 1.1HP gain, and a 0.4ft-lb LOSS, on a 300+rwHP 96 Z28. I have also seen one case where an indiivual documented a 2.5MPG loss in fuel mileage, simply from removing the screen.... put it back in, the mileage went back up, took it out, the mileage went back down. Only one case in thousands, but I'd keep the screen so that if I noticed a drop in fuel mileage, or a rough idle, I'd put it back in.

JMHO.

S.J.S.

Dude...simple answer. You took it out....dump it! I did 4 years ago with no regrets nor problems.

94formulabz

Let me ask you this, is the MAF an analog signal, or what is the sampling rate?

I still feel that removing a restriction does not change the calibration. Now removing a device which promotes laminar flow does reduce the precision of the instrument, but not the accuracy because your going to get the same avg result, just with more noise or varibility in the signal. The calibration curve will be the same though for both scenarios, one will just be more precise. You are definitly right though, there is a potential negative effect. The question is does it reduce the precision enough and does the computer make adjustments fast enough to actually make a difference.

Keep in mind i only removed mine last week when i cleaned the MAF. I had removed it once before right when i got the car but decided to put it back in because i didn't think it would gain me anything and 'it must be there for a reason'. I am running a symetrical straight ram air setup so that contributed to me ultimately removing it. I did keep it just like all my old parts

ANother reason for removing it was because Bryan of PCMforless said to go ahead with it, not because he felt it would be a gain, but because it doesn't hurt. He said he finds very poor calibrations on aftermarket MAFs and obviously home ported ones, ha. He has no problems with screen removal hurting the calibration.

I think another thing to keep in mind is that all that for all the people who claim their performance decreased, ther eare just as many people claiming they felt a performance increase. We know factually that the latter is not true because noone can tell 1 hp. You get much larger variations from engine and intake air temperatures. We we can't rule out that people didn't have decrease in performance which is a strong arguement against removing it. You do say 1 hp, but also 2.5 mpg decrease. I don't think everyone losed 2.5 mpg, or less people would do it. Your right it's probably not worth it, but many people do it without problems, not that that makes it right......

-brent

-brent

Injuneer

The electronics in the sensor convert the info from the wheatstone bridge circuit to a variable frequency output signal. In the PCM, there is a calibration table of frequency vs. gps
You're entitled to your opinion. I'm basing mine on 40+ years of engineering experience, much of it dealing with process control instrumentation, and also on experience with modeling the dynamics of air flow systems, with particular emphasis on flow distribution measurements, and promoting flow velocity uniformity to maximize the performance of electrostatic precipitators.

I also have the benefit of having recieved literally 100's of PCM scans, with requests for assistance in solving problems, and I have been able to trace many of these problems to MAF alteration.
The device doesn't "promote laminar flow".... it promotes a uniform flow distribution (velocity) across the open area of the meter, in both the laminar and turbulent regimes.
You seem to be basing your argument on the difference in meaning of the words accuracy and precision. They are, in fact synonyms. Might want to clarify your point.
After reading threads on this argument over more than 5 years, on the 3 boards where I moderate the LT1 Tech, Advanced Tech and other F-Body forums, I can tell you that about 1/3 of the people feel nothing; 1/3 get miraculous SOTP gains that are not backed up with dyno or track results, and 1/3 have "problems".
That would be "I don't thing everyone lost 2.5mpg." And I didn't say everyone did. I said "I have seen one case"..... After seeing the way many people throw around terms like "miles per tank", and the number of people that don't really know how to calculate their fuel mileage, I doubt most people even attempt to relate their loss of mileage to the alteration of the MAF. .

This whole subject really isn't worth arguing about in my mind. I was simply trying to present some factual information that might help some people make up their minds. I really don't care whether anyone takes the screen out or whether they leave it in... it's their car, they can do what they want with it, and if they are happy, so be it. Just trying to "present the facts".

I ran my bolt-on motor for 5 years with the MAF sensor intact. I was happy. Now I don't even use an MAF sensor, so I'm not sure why I even look at threads on the subject .

Fred

94formulabz

Fred, i'm not trying to be arguementative, and we are all probably overanalyzing the situation. Precision and accuracy DO have two distinctly different meanings, not synonomous. Accuracy is the relationship to the true value. You can have a device with a lot of 'noise' in the signal or variabililty and it is still accurate. It is accurate if the avg value it outputs is in agreement with the true value. Precision describes the stability of the signal or repeatability of the sampling.

Lets use the example of shooting a gun, you put 5 bullets within a 1 inch radius. That is very precise. You may be 6" away from the bullseye of the target though in which case your accuracy was not very good, you had a grouping somewhat away from the target or true value. In a second scenario you could have 1 shot dead center, two 4" above and two shots 4" below. Your Accuracy would be perfect because the average value is the true value that you were aiming for. On the other hand your precision is not very good because your grouping spanned 8".

You still have not said anything to lead me to believe that the accuracy of the MAF has been affected. Yes you have introduced noise into the signal and hurt its precision slightly, but the calibration curve it uses is still the same because the signal is jumping around the true value.

The next question is what is the response time of the PCM. The adjustments it makes based on the MAF signal jumping around slightly due to the increased turbulence are in my mind minor. If there is turbulence which causes the MAF to output a high signal, it will be followed by a low signal which averages to the true velocity mean. You may be causing the signal to jump around slightly, but since it hovers around the true value it is probably not enough to destabilize the PCM.

All this headache over 1.1 hp! arrrrgh, everyone keep their damn screens on . The flow numbers the other Brent posted seem to make a case for removing it since it's free and many people don't experience any negative effects. I'm not pushin a restrictive number of CFM yet, but even at lower flows there is a tiny pressure drop accross it and every little bit helps.

Good discussion though Fred, sorry to drag you into this. I work testing components for the electronics industry, so i'm not totally pulling stuff out of my *** here. I don't have 40 yrs exp though

94formulabz

Alterations meaning descreening, or descreening and porting? We can theorize all day, but if your telling me you can see in the PCM logs maf descreening caused the problem than that real life experience, which is ultimately what matters, is enough to make me shut the hell up

P.S. i strongly disagree about precision and accuracy sharing the same meaning as mentioned in the above thread. I can agree to the fact that they are commonly misused and interchanged in laymans terms though.

-Brent