Cobb AccessPORT Discussion
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Joined: Jul 2002
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From: portland oregon
of course this is with the stock calibration of the stock MAF. stick the stock MAF in a different sized housing and its going to be a percentage off high(for a smaller housing) or low(for a larger one) thats why if you buy an aftermarket MAF from a reputable supplier they will have flowed the meter and provide you with the proper calibrations for tuning
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From: Mesa, Arizona
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Joined: Dec 2006
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From: Lake County, Illinois
This may be a no-brainer for some, but it had me scratching my head for a while....cause I'm a novice 
My LTFT readings were all over the place with each map I tried. On MM's 1_0 map, the LTFT would settle to 22 at idle, and drop to about 6 under load. I tried pretty much all of the "a" series in an attempt to lower the LTFT but nothing worked.
Here's what I did....simple really. I cleaned _ALL_ of the **** out of my intake. I cleaned everything between the throttle body to the VFAD actuator. I picked up a can of MAF Sensor Cleaner and a can of Engine Degreaser from Pep Boys. My MAF sensor was filthy due to lots of construction around here for years. I must have used a third of the can cleaning the MAF sensor before I was satisfied. Oil had collected in the ridges on the rubber air duct, so I degreased it and wiped everything clean. Black residue had accumulated on the two screens before the MAF sensor, so those got a good cleaning as well. To top it off, I had a spare air filter so I threw it in there.
Now on the same tune my idle LTFT is 12.5, and it drops to 1.6 under load. My STFT is stable and doesn't exceed 15 in either direction under normal conditions.
My LTFT readings were all over the place with each map I tried. On MM's 1_0 map, the LTFT would settle to 22 at idle, and drop to about 6 under load. I tried pretty much all of the "a" series in an attempt to lower the LTFT but nothing worked.
Here's what I did....simple really. I cleaned _ALL_ of the **** out of my intake. I cleaned everything between the throttle body to the VFAD actuator. I picked up a can of MAF Sensor Cleaner and a can of Engine Degreaser from Pep Boys. My MAF sensor was filthy due to lots of construction around here for years. I must have used a third of the can cleaning the MAF sensor before I was satisfied. Oil had collected in the ridges on the rubber air duct, so I degreased it and wiped everything clean. Black residue had accumulated on the two screens before the MAF sensor, so those got a good cleaning as well. To top it off, I had a spare air filter so I threw it in there.
Now on the same tune my idle LTFT is 12.5, and it drops to 1.6 under load. My STFT is stable and doesn't exceed 15 in either direction under normal conditions.
Mu ha.. ha...
Joined: Aug 2004
Posts: 14,361
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From: Cali
Jeff and I were just talking about formula conversions and we discussed the idea that each g/sec is about 1.23-1.3 h.p. That would bring into question the accuracy of something(either the math, MAF or Cobb) in this case as I doubt your engine is making 460+ h.p. Of course that is the raw h.p. which would include the power needed to move the weight of the engine's parts themselves, so
. It'd be cool to get your car on a dyno in 4th gear and look at the data.
. It'd be cool to get your car on a dyno in 4th gear and look at the data.I think it was ULLOSE who tested the Cobb last year and said he got 222 to the rear wheels.
Depending on the amount of air flowing past a wire it sends a voltage to heat it or something I don't know. I don't make maf sensors...
I guess it measures velocity assuming air density is constant..., but it probably wont be. I worded my previous post poorly. I can like see stuff in my head man, but like I don't know sometimes its like hard to make that picture into words man, you like know what I mean hombre?
I still don't see how you will get higher readings from a larger tube?
I guess it measures velocity assuming air density is constant..., but it probably wont be. I worded my previous post poorly. I can like see stuff in my head man, but like I don't know sometimes its like hard to make that picture into words man, you like know what I mean hombre?
I still don't see how you will get higher readings from a larger tube?
http://en.wikipedia.org/wiki/Mass_flow_sensor
A smaller tube would have higher flow through it than expected...therefore higher MAF readings for total flow IE MAF would think there was more total flow through it
A larger tube would have less flow through it for amount of total flow...
Is there an inverse relationship in there I'm missing??
This may be a no-brainer for some, but it had me scratching my head for a while....cause I'm a novice
My LTFT readings were all over the place with each map I tried. On MM's 1_0 map, the LTFT would settle to 22 at idle, and drop to about 6 under load. I tried pretty much all of the "a" series in an attempt to lower the LTFT but nothing worked.
Here's what I did....simple really. I cleaned _ALL_ of the **** out of my intake. I cleaned everything between the throttle body to the VFAD actuator. I picked up a can of MAF Sensor Cleaner and a can of Engine Degreaser from Pep Boys. My MAF sensor was filthy due to lots of construction around here for years. I must have used a third of the can cleaning the MAF sensor before I was satisfied. Oil had collected in the ridges on the rubber air duct, so I degreased it and wiped everything clean. Black residue had accumulated on the two screens before the MAF sensor, so those got a good cleaning as well. To top it off, I had a spare air filter so I threw it in there.
Now on the same tune my idle LTFT is 12.5, and it drops to 1.6 under load. My STFT is stable and doesn't exceed 15 in either direction under normal conditions.
My LTFT readings were all over the place with each map I tried. On MM's 1_0 map, the LTFT would settle to 22 at idle, and drop to about 6 under load. I tried pretty much all of the "a" series in an attempt to lower the LTFT but nothing worked.
Here's what I did....simple really. I cleaned _ALL_ of the **** out of my intake. I cleaned everything between the throttle body to the VFAD actuator. I picked up a can of MAF Sensor Cleaner and a can of Engine Degreaser from Pep Boys. My MAF sensor was filthy due to lots of construction around here for years. I must have used a third of the can cleaning the MAF sensor before I was satisfied. Oil had collected in the ridges on the rubber air duct, so I degreased it and wiped everything clean. Black residue had accumulated on the two screens before the MAF sensor, so those got a good cleaning as well. To top it off, I had a spare air filter so I threw it in there.
Now on the same tune my idle LTFT is 12.5, and it drops to 1.6 under load. My STFT is stable and doesn't exceed 15 in either direction under normal conditions.
Check for a leak on the intake tract after the MAF. I was having similar problems. My LTFT was hovering around 12-16 at idle and would drop to about 1 or so when I was driving. I found that I had a leak on the intake. I sealed it up and my LTFT immediately dropped to 1 and my STFT has been pretty steady at -1 to -2 on MM1.3a.
Cel
Last edited by Celronx; Mar 31, 2008 at 10:25 AM.
Ok...I know I'm on holidays...and Mickey has me kinda reeling from all the hype...but pls explain...
A smaller tube would have higher flow through it than expected...therefore higher MAF readings for total flow IE MAF would think there was more total flow through it
A larger tube would have less flow through it for amount of total flow...
Is there an inverse relationship in there I'm missing??
A smaller tube would have higher flow through it than expected...therefore higher MAF readings for total flow IE MAF would think there was more total flow through it
A larger tube would have less flow through it for amount of total flow...
Is there an inverse relationship in there I'm missing??
Cel
I think I got it.
Bigger pipe equals higher pressure based on Bernoulli's equation.
Higher pressure means the MAF will see higher density air or less heat in the wire.
Am I close?
Cel
Bigger pipe equals higher pressure based on Bernoulli's equation.
Higher pressure means the MAF will see higher density air or less heat in the wire.
Am I close?
Cel
. On MM's 1_0 map, the LTFT would settle to 22 at idle, and drop to about 6 under load. I tried pretty much all of the "a" series in an attempt to lower the LTFT but nothing worked.
Now on the same tune my idle LTFT is 12.5, and it drops to 1.6 under load. My STFT is stable and doesn't exceed 15 in either direction under normal conditions.
Now on the same tune my idle LTFT is 12.5, and it drops to 1.6 under load. My STFT is stable and doesn't exceed 15 in either direction under normal conditions.
Has nothing to do with pressure....it has to do with airflow over the wire in the small area that it tests....more flow causes the resistance to drop in the wire...and MAF voltage to go up....
I hate quoting Wikipedia, but oh well. This part of the link above is what got me thinking about pressure.
"If air density increases due to pressure increase or temperature drop, but the air volume remains constant, the denser air will remove more heat from the wire indicating a higher mass airflow"
This and the part of Bernoulli's principal that states that the same amount of fluid (air) flow through a larger pipe will have a higher pressure, or a lower pressure through a smaller pipe got me on this path. Volume going into the engine would remain the same, only the pressure would be different.
Cel
"If air density increases due to pressure increase or temperature drop, but the air volume remains constant, the denser air will remove more heat from the wire indicating a higher mass airflow"
This and the part of Bernoulli's principal that states that the same amount of fluid (air) flow through a larger pipe will have a higher pressure, or a lower pressure through a smaller pipe got me on this path. Volume going into the engine would remain the same, only the pressure would be different.
Cel
Doppelgänger
Joined: Feb 2008
Posts: 3,192
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From: Florida
Local shop just quoted me $50 to ceramic coat the intake pipe (in black). I don't have time right now to leave them the intake piping for a few days, so I plan on wrapping the maf piping up with a reflective thermal blanket and see if it's worthwhile to ceramic coat. I bet it is... so this will hold me off for a week or two till I can get it coated properly.
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Joined: Dec 2006
Posts: 60
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From: Lake County, Illinois
Check for a leak on the intake tract after the MAF. I was having similar problems. My LTFT was hovering around 12-16 at idle and would drop to about 1 or so when I was driving. I found that I had a leak on the intake. I sealed it up and my LTFT immediately dropped to 1 and my STFT has been pretty steady at -1 to -2 on MM1.3a.
Cel
Cel
The numbers I posted are after only one drive cycle. I did some data logging last week before cleaning things up on 1_0. I had changed over to 1_2a on Friday hoping the logs would show me a difference. Then on Sunday I cleaned everything and re-flashed 1_0 so I could compare future logs to my "before cleaning" results from last week.
I'm going to leave this one on till the end of the week and see how much the trims change between "Day 0" and "Day 5". I'll change the map one last time after some more logging on Friday.
Power!!
Joined: Feb 2004
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From: Sunny See attle
I will throw my $0.02 in here and see if I am close.
1st law of Thermo says Mass in=mass out (or garbage whatever you're flowing).
Mass flow rate of an incompressible fluid (which is what we have in the intake tube) is density*cross sectional area*velocity. Rho*A*V (make sure your units are consistent! (inches or feet but not both at the same time)
In this case the MAF "knows" the Density from the temperature and Baro sensors, and it "knows" the size of the pipe (pre-programmed fixed value) so from the cooling effect of the air it can determine the velocity based on some basic heat transfer calculations and the known temp. of the air.
What happens is when you change the diameter of the pipe (the A in Rho*A*V) you affect the velocity inversely and the PCM doesn't know it since there is no "pipe diameter sensor." So the velocity slows down and the PCM should think there is less air going in then there actually is.
Only thing is from the previous posts it sounds like Phil is seeing a higher than actual recorded flow rate rather than lower.
So if that's the case...I dunno
1st law of Thermo says Mass in=mass out (or garbage whatever you're flowing).
Mass flow rate of an incompressible fluid (which is what we have in the intake tube) is density*cross sectional area*velocity. Rho*A*V (make sure your units are consistent! (inches or feet but not both at the same time)
In this case the MAF "knows" the Density from the temperature and Baro sensors, and it "knows" the size of the pipe (pre-programmed fixed value) so from the cooling effect of the air it can determine the velocity based on some basic heat transfer calculations and the known temp. of the air.
What happens is when you change the diameter of the pipe (the A in Rho*A*V) you affect the velocity inversely and the PCM doesn't know it since there is no "pipe diameter sensor." So the velocity slows down and the PCM should think there is less air going in then there actually is.
Only thing is from the previous posts it sounds like Phil is seeing a higher than actual recorded flow rate rather than lower.
So if that's the case...I dunno
Momentum Keeps Me Going
Joined: Sep 2002
Posts: 5,036
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From: Colorado
Is the temp sensor ambient air or is it temp in the tube? Wouldn't the varing air temp from different intakes make this sensor wrong if it's not 'in the tube temp'?
And if the air is under pressure (boosted) wouldn't the baromentric sensor be useless, or if there is any ram air effect at 100+ like say with the RB duct?
And if the air is under pressure (boosted) wouldn't the baromentric sensor be useless, or if there is any ram air effect at 100+ like say with the RB duct?
Power!!
Joined: Feb 2004
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From: Sunny See attle
Now if it's a push through and the air has been compressed already then you are right the Rho is now off in the formula since it doesn't have an in tube Baro sensor.
