Ask twice,purchase once.............
Le Mans Master
Joined: May 2006
Posts: 5,987
Likes: 18
From: DuBois PA
St. Jude Donor '11-'12-'13-'14-'15
More accurate is probably technically correct, but that doesn't always mean it's a good thing either.
The sensor itself (in theory) should read the airflow more accurately near the throttle body, as the air flow through it will be straighter (more laminar), and less turbulent as opposed to placed right by the airbox or filter.
But, consider the MAF calibration within the PCM tune, is a lookup table of static values. (x g/sec of airflow = x hz).
By making the MAF "more accurate", only means the actual airflow now corresponds to a different frequency (hz) that the MAF reports to the PCM.
If you do not re-plot the MAF calibration to reflect those changes, then the only thing you accomplished is made engine fueling more inaccurate, because now the PCM is now receiving incorrect airflow information, even though the sensor itself may be reading the airflow better.
And the MAF is a big player in how the PCM fuels the engine.
I'm sure the Vararam (and Callaway and Halltech) and any other system that was designed to relocate the MAF has been designed with this in mind, and are such that no tuning changes are "required"...but changing anything with the MAF, even screen removal, will alter the readings it reports to the PCM. Sometimes for the good, sometimes the other way....but never "more accurate" unless recalibration was also done.
The sensor itself (in theory) should read the airflow more accurately near the throttle body, as the air flow through it will be straighter (more laminar), and less turbulent as opposed to placed right by the airbox or filter.
But, consider the MAF calibration within the PCM tune, is a lookup table of static values. (x g/sec of airflow = x hz).
By making the MAF "more accurate", only means the actual airflow now corresponds to a different frequency (hz) that the MAF reports to the PCM.
If you do not re-plot the MAF calibration to reflect those changes, then the only thing you accomplished is made engine fueling more inaccurate, because now the PCM is now receiving incorrect airflow information, even though the sensor itself may be reading the airflow better.
And the MAF is a big player in how the PCM fuels the engine.
I'm sure the Vararam (and Callaway and Halltech) and any other system that was designed to relocate the MAF has been designed with this in mind, and are such that no tuning changes are "required"...but changing anything with the MAF, even screen removal, will alter the readings it reports to the PCM. Sometimes for the good, sometimes the other way....but never "more accurate" unless recalibration was also done.
I always thought that the MAF signal was in essence a dynamic input to the PCM and could in fact be "re-learned"... Now I've gotts re-learn something!
Tim
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
Help me out here, The PCM uses the MAF signal to verify a static table that it then uses to determine air/fuel mixtures for the engine?
I always thought that the MAF signal was in essence a dynamic input to the PCM and could in fact be "re-learned"... Now I've gotts re-learn something!
Tim
I always thought that the MAF signal was in essence a dynamic input to the PCM and could in fact be "re-learned"... Now I've gotts re-learn something!
Tim
So, let's say your car is idling, and the MAF is sending a 3000hz signal to the PCM. How does the PCM interpret that to be airmass?
By looking at a pre-programmed table which attaches a specific frequency to a specific air mass value. (These mass values are programmable, but are static once loaded into the PCM).
As an example, here is a MAF calibration table that corresponds the two:
Code:
MAF Sensor Calibration (Grams/Second) Hz Value 1500 1.476563 1625 1.796875 1750 2.125000 1875 2.492188 2000 2.890625 2125 3.328125 2250 3.804688 2375 4.335938 2500 4.906250 2625 5.539063 2750 6.218750 2875 6.945313 3000 7.726563 3125 8.562500 3250 9.453125 3375 10.382813 3500 11.375000 3625 12.445313 3750 13.601563 3875 14.851563 4000 16.210938 4125 17.703125 4250 19.320313 4375 21.015625 4500 22.773438 4625 24.539063 4750 26.429688 4875 28.414063 5000 30.492188 5125 32.664063 5250 34.953125 5375 37.359375 5500 39.898438 5625 42.617188 5750 45.484375 5875 48.500000 6000 51.664063 6125 54.976563 6250 58.437500 6375 62.054688 6500 65.820313 6625 69.734375 6750 73.804688 6875 78.031250 7000 82.406250 7125 86.937500 7250 91.632813 7375 96.492188 7500 101.507813 7625 106.710938 7750 112.093750 7875 117.632813 8000 123.351563 8125 129.242188 8250 135.296875 8375 141.531250 8500 147.867188 8625 154.414063 8750 161.148438 8875 168.078125 9000 175.218750 9125 182.578125 9250 190.226563 9375 198.210938 9500 206.343750 9625 214.796875 9750 223.523438 9875 232.523438 10000 241.828125 10125 251.343750 10250 261.132813 10375 271.187500 10500 281.531250 10625 292.148438 10750 303.054688 10875 314.250000 11000 325.734375 11125 337.507813 11250 349.585938 11375 361.960938 11500 374.640625 11625 387.625000 11750 400.921875 11875 414.531250 12000 428.460938
So my earlier-stated point was....What happens when you physically modify the MAF in any manner, or make it "more accurate" that it now takes 8.2 g/s airmass for the MAF to ring at 3000hz?
Without changing the above table in the tune to reflect the hardware changes made, the PCM still only "sees" 7.7 g/s entering the engine. And thus, fuels the engine too lean.
As a further example, the above MAF table shown above is factory stock for a 2001 C5, which uses the 85mm MAF sensor with screen.
In comparison, here is the stock table for a 2002 Z06, which uses the same actual MAF sensor, same 85mm housing, the only difference being the 02 Z06 sensor does not have the laminar screen attached to it:
Code:
MAF Sensor Calibration (Grams/Second) Hz Value 1500 1.421875 1625 1.757813 1750 2.101563 1875 2.484375 2000 2.859375 2125 3.257813 2250 3.695313 2375 4.179688 2500 4.710938 2625 5.312500 2750 5.968750 2875 6.679688 3000 7.429688 3125 8.226563 3250 9.078125 3375 9.968750 3500 10.914063 3625 11.929688 3750 13.054688 3875 14.273438 4000 15.585938 4125 16.984375 4250 18.468750 4375 20.046875 4500 21.718750 4625 23.476563 4750 25.335938 4875 27.281250 5000 29.335938 5125 31.484375 5250 33.742188 5375 36.109375 5500 38.617188 5625 41.296875 5750 44.171875 5875 47.203125 6000 50.398438 6125 53.765625 6250 57.296875 6375 61.007813 6500 64.875000 6625 68.914063 6750 73.117188 6875 77.468750 7000 81.968750 7125 86.632813 7250 91.453125 7375 96.429688 7500 101.585938 7625 106.898438 7750 112.359375 7875 118.007813 8000 123.828125 8125 129.843750 8250 136.046875 8375 142.476563 8500 149.125000 8625 155.984375 8750 163.062500 8875 170.375000 9000 177.921875 9125 185.703125 9250 193.726563 9375 201.992188 9500 210.515625 9625 219.296875 9750 228.335938 9875 237.640625 10000 247.226563 10125 257.062500 10250 267.164063 10375 277.562500 10500 288.250000 10625 299.250000 10750 310.554688 10875 322.195313 11000 334.156250 11125 346.492188 11250 359.164063 11375 372.218750 11500 385.656250 11625 399.507813 11750 413.765625 11875 428.453125 12000 443.601563
This is why many people run into issues when doing the "performance" mod of descreening their MAF. They might not be changing the actual airmass into the engine much (if at all), but they sure are tricking the PCM, by altering the sensor's ability to sense that airmass.
Last edited by Y2Kvert4me; Aug 24, 2009 at 08:44 PM.
Safety Car
Joined: May 2008
Posts: 4,237
Likes: 11
From: Lacombe Louisiana
The PCM still only "sees" what the MAF is actually reading and sending to it,it will adjust mixture from that reading along with several others,MAP, RPM,air temp,eng temp etc.It also has adaptive capabilities so those tables are not set in stone.
Le Mans Master
Joined: May 2006
Posts: 5,987
Likes: 18
From: DuBois PA
St. Jude Donor '11-'12-'13-'14-'15
This is cool, I'm learning alot more about the role the MAF plays in the bigger picture. I know we're digressing from the OP's original question and I hope he doesn't mind....
If I'm understanding all this great info correctly... relocating the MAF MAY change it's input to the PCM and (technically) may reflect a more accurate reading of the actual laminar airflow hitting the TB. Assuming the airstream had a chance to settle down while traversing the bridge/coupler... Note: I think this may be more accurate for people using the twin cone assemblies.
Now this new signal may not be accurate due to the static translation table stored in the PCM right? This is where I was getting confused... I thought that table was dynamic, in other words would eventually be adjusted to account for the changes in the upstream O2 sensors outputs, as an example...
I find it interesting that the tables are different for different vehicles... Airmass is airmass after all no matter what motor it's being sucked into. I suppose it's another area that can be tweaked for tuning purposes though...
Thinking more about this, it might make more sense to relocate the temp sensor closer to the TB to take into account heat soak from the engine... I wonder what THAT would screw up????
Tim
If I'm understanding all this great info correctly... relocating the MAF MAY change it's input to the PCM and (technically) may reflect a more accurate reading of the actual laminar airflow hitting the TB. Assuming the airstream had a chance to settle down while traversing the bridge/coupler... Note: I think this may be more accurate for people using the twin cone assemblies.
Now this new signal may not be accurate due to the static translation table stored in the PCM right? This is where I was getting confused... I thought that table was dynamic, in other words would eventually be adjusted to account for the changes in the upstream O2 sensors outputs, as an example...
I find it interesting that the tables are different for different vehicles... Airmass is airmass after all no matter what motor it's being sucked into. I suppose it's another area that can be tweaked for tuning purposes though...
Thinking more about this, it might make more sense to relocate the temp sensor closer to the TB to take into account heat soak from the engine... I wonder what THAT would screw up????
Tim
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
Compare the two factory MAF curves above....study them very closely.
They flip-flop right at 7500hz.
Below 7500hz, the screened MAF is more sensitive....reporting MORE airmass at any given frequency. (7.72 g/s vs 7.42 g/s @3000hz).
Above 7500hz, the screenless unit is reporting more airmass at a given frequency....and dramatically so above 9000hz.
So, why are these two MAF curves so very different? If you remove the screen from your LS1 MAF, and don't replot the MAF curve, what you're claiming everything would remain the same, and that is absolutely incorrect.
Think of it a simpler way....
Your speedometer tells you how fast the car is traveling, right?
Is there any physical change you could make that would alter the ability of the speed sensor to provide an accurate reading of that rate of travel? Like maybe tire size? Would that change the indicated speed, or would it not change?
That may seem like a silly comparison....of course a tire diameter difference will alter indicated speed.
Just the same as altering flow pattern will affect the MAF's ability to measure airmass. Both are cases of altering sensor sensitivity by means of mechanical change.
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
The temps of the air charge into the cylinder is not determined solely by IAT. The PCM blends the IAT value with ECT. (engine coolant temp).
For the exact reason you describe. At low airmass rates into the engine, it is expected the air will get heated up by the engine prior to filling the cylinder...at this point, air charge is considered to be very close to ECT.
At high rates of flow into the engine, IAT is the more dominant decider of charge air temp.
In between, the PCM blends the two temp inputs together and decides the happy medium.
Thread Starter
Drifting
Joined: Apr 2005
Posts: 1,545
Likes: 3
From: CLIFTON PARK NY
Ummmmmmmmmmm,OK,so what will it do again,lol! So installing a different powerduct(Vararam)which allows the relocation of the MAF,WILL cause the car to run leaner within peramiters,but not necessarily cause any codes,even though a tune has been programmed prior to the change in MAF sensor? For better understanding of this,is my language,lol,im waiting to receive the vararam duct to install it then ill take a ride over to my buddies at Cartek and see what changes have occured,if any and will report back,hopefully with a before and after difference in mass readings,thanks once again guys!
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Safety Car
Joined: May 2008
Posts: 4,237
Likes: 11
From: Lacombe Louisiana
The differences in those two MAF tables would prob be more accurately attributed to the smoother air flow of the one with the screen and more turbulence from the one without ,making it's out put signal vary more. Putting you MAF closer to your TB will NOT in itself make it run lean nor rich.Since your injectors are adjusted in milliseconds and are monitored by your O2 sensors,if you are lean or rich it is prob caused by something other than the relocation.The Vararam duct has a sort of lousy connector which if not done properly can cause an air leak between MAF and TB which will cause issues.Going to the track tonite to see if the duct makes any difference over the stocker though I dont feel anything SOTP.
Instructor
Joined: Jul 2009
Posts: 164
Likes: 0
From: Ft. Worth, The Lone Star State
**subscribed**
Dam!! I learned so much about MAF just by reading this small thread, you guys are very helpfull and informative
well I just ordered a Halltech air flow straitner (that was just before reading this). I too have been getting lean code DTC's with a Veraram intake only (stock port duct).
Im hoping this will lessen the turbulance created, thus less vibrations on the MAF sensors resulting in false readings (so-to-speak). Ill be putting these ''no more codes'' testimonials to the test myself, and see how it goes.
I will also check, and double check my connections again to make sure I have no leaks before, and after installation.
Thanks,
Dam!! I learned so much about MAF just by reading this small thread, you guys are very helpfull and informative
well I just ordered a Halltech air flow straitner (that was just before reading this). I too have been getting lean code DTC's with a Veraram intake only (stock port duct).
Im hoping this will lessen the turbulance created, thus less vibrations on the MAF sensors resulting in false readings (so-to-speak). Ill be putting these ''no more codes'' testimonials to the test myself, and see how it goes.
I will also check, and double check my connections again to make sure I have no leaks before, and after installation.
Thanks,
Race Director
Joined: Oct 2002
Posts: 16,477
Likes: 26
From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
Locating the MAF up near the TB will have the same basic effect as the screen does...the airflow at that point of the intake tract will be "straighter" and less turbulent than it is exiting the airbox/filter. Thus, the reported frequency value to the PCM WILL change more than the actual airmass entering the engine did.
Putting you MAF closer to your TB will NOT in itself make it run lean nor rich.
That is something that can easily be scanned, logged and proven. If not by monitoring the airmass itself, the change in fuel trims should be clear evidence of it.
The basic premise and goal of tuning is to get the base fueling as accurate as possible, with trims as close to zero as possible. Making any airmass change, without tuning for it, is going in the wrong direction towards achieving that goal.
Thread Starter
Drifting
Joined: Apr 2005
Posts: 1,545
Likes: 3
From: CLIFTON PARK NY
Ok,this last post made more sense to me to sum it all up! Realistically,gain of power or better running isnt my goal by changing to a vararam power duct opposed to a halltech,Basically i found lost money and i wanted to have a complete vararam set up instead of a mix match with half vararam and half halltech lol,I know,call me ****,but the only thing i was curious of if the relocation of the MAF would set a code,other than that,i learned a whole lot more on how a MAF works,thanks to the men,and women,if any,that voutured their input!
Melting Slicks
Joined: Nov 2008
Posts: 2,938
Likes: 65
From: Rochester Hills MI
i think having the maf on the filter side of the air bridge will be reading a more turbulant flow, but a more uniform flow. if it is right next to the throttle body, the air flows towards the top and bottom of the butterfly valve in any case that is not WOT. the flow is most definitley more laminar, but it is probably concentrated on the top and bottom of the maf in these cases. personally, i would choose the turbulent, but more uniform flow over the laminar flow with less uniformity. i think the maf screen probably does a pretty good job of making the flow laminar anyways. just my 2 cents.
Drifting
Joined: Sep 2008
Posts: 1,410
Likes: 2
From: Chicago IL
So the bottom line is, ducts are all waste of money? Whether it relocates the MAF or not, it really doesn't matter?
Because when you move MAF near TB, the table is now inaccurate, and if you adjust the values of the table (by the tuner), aren't you just recorrecting what was right in the first place?
GM obviously understood these concepts and when they created the table, they probably had taken in account of the MAF being in the front already.
Because when you move MAF near TB, the table is now inaccurate, and if you adjust the values of the table (by the tuner), aren't you just recorrecting what was right in the first place?
GM obviously understood these concepts and when they created the table, they probably had taken in account of the MAF being in the front already.
Safety Car
Joined: May 2008
Posts: 4,237
Likes: 11
From: Lacombe Louisiana
I went to the track last night and ran my best personal time,12.79. My best before the power duct was 12.82.So really no difference as lower ambient temps could have made the difference.I will say I improved about 1.5 mpg at steady 75 mph cruise and my idle quality is better. Funny my car threw a code with just the vararam and stock air bridge with a smooth bellows 0101 if I remember correctly and that has gone away with the power duct.
Instructor
Joined: Jul 2009
Posts: 164
Likes: 0
From: Ft. Worth, The Lone Star State
If It fails, I will try the power duct and see if I can get similar results to you rebelheart.
I was just a little hesitant to move the MAF closer to the throttle body, as thats the way GM engineers set the car up with it up front. will see...
Tech Contributor
Joined: May 2008
Posts: 2,843
Likes: 16
From: Howell Michigan
St. Jude Donor '09-'10-'11
Ok, I can understand the possibility that change the throttle body and upstream induction system could improve your track time while running at WOT. I’m having a hard time buying the fuel economy claim. To that, let me explain why I feel that way and if you see something I have wrong please point it out:
Let’s assume the 75 mile an hour steady speed and let’s leave the meteorological factors out of the example to keep it as simple as possible.
To maintain the Corvette rolling down the road 75 mph I have to overcome a number of forces. They include aerodynamic load, road friction (tires to road surface) and other drivetrain parasitic loads. These forces add up to a power requirement to keep everything in balance and maintain the car at 75 mph. There are a few things that might be changed to reduce these forces. I could change tire pressure which will change rolling resistance, or, reducing parasitic loads like the water pump, air-conditioning compressor, alternator, etc.. I could also change mechanical components of the engine to improve combustion efficiency, like spark timing, and compression ratio.
The throttle plate regulates the engines power output and the output needed is set by the drag to the vehicle while maintain the car at the 75 mph speed. I see no correlation with the inlet system before the throttle plate in this 75 mph example.
Safety Car
Joined: May 2008
Posts: 4,237
Likes: 11
From: Lacombe Louisiana
If you make a bit more power and it takes a bit less throttle opening to maintain that speed you will see an improvement in mpg.Was the duct and MAF relocation the cause of this? Who knows,could just as well of been the 10 degree cooler ambient temp.I am just reporting what I saw on my cars readout on a 50 mile straight line,cruise control on trip to the track. But the lack of that MAF code reappearing and the better idle quality are facts.