Upgrading MAF question
11-24-2010, 07:32 AM
#1
3rd Gear Member
Thread Starter
Join Date: May 2007
Location: OH
Posts: 564
Upgrading MAF question
Hey guys, I recently came accross a Granatelli MAF with 24lb Calibration and was wondering if it would be worth my time to put on my car.
I currently have a KB 2.1 s/c installed on my 96GT with the stock MAF. I used sniper tuning to tune the car. Everything seems to be ok, but I know KB recommends upgrading the MAF to at least 80mm. This Granatelli MAF I have is 90mm.
The only thing I am wondering is since the KB 2.1 comes with 36lb injectors, and this MAF is calibrated to 24lb, will that be ok? I can use sniper to tune it, but am just wondering if it is worth the time or if I should just go buy one that is calibrated for 36lb injectors.
I currently have a KB 2.1 s/c installed on my 96GT with the stock MAF. I used sniper tuning to tune the car. Everything seems to be ok, but I know KB recommends upgrading the MAF to at least 80mm. This Granatelli MAF I have is 90mm.
The only thing I am wondering is since the KB 2.1 comes with 36lb injectors, and this MAF is calibrated to 24lb, will that be ok? I can use sniper to tune it, but am just wondering if it is worth the time or if I should just go buy one that is calibrated for 36lb injectors.
11-24-2010, 08:33 AM
#2
5th Gear Member
Join Date: Nov 2005
Location: MN
Posts: 4,412
Well I wouldn't buy a Granatelli MAF first of all... but the injector calibration is in your EEC, not your MAF. Your MAF doesn't care what your injectors are. Are you currently pegging (or close to pegging) your stock MAF? If not, don't worry about it. If you are, just get yourself a lightning MAF and call it a day.
11-24-2010, 09:16 AM
#3
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
As Moose said, a "calibrated" MAF is not calibrated to just a specific injector capacity--but rather to a specific injector capacity AND a specific tune's MAF Transfer Function (MTF).
If the Granatelli MAF you have acquired was intended to be used on a '96 GT then it will have been "calibrated" to work with 24lb/h injectors and an unmodified '96 GT tune. The calibration part is that the MAFs output curve has been adjusted to trick the unmodified tune into believing that less air is flowing than really is.
I.e. the calibrated MAF is a kludge left over from years ago when tunes could not be easily (or at all) modified, and when engine modifications required more air than the stock MAF could flow (it was "pegged") and more fuel at WOT.
The tune doesn't know that larger injectors have been installed, so it calculates a shorter injector pulse because of the MAF's lie. A shorter pulse with larger injectors = the proper amount of fuel. As air flow increases the MAF lies less and less, and the PCM starts to calculate "normal" pulse widths which with the larger injectors (larger than the tune thinks they are) deliver more fuel.
To use that MAF with your car you will need to determine its real transfer function, and load that into your tune, and then probably tweak it quite a bit because the shape of the "calibrated" MAF's transfer curve will be quite different from that of a non-calibrated MAF's curve; which is what the tune expects when it interpolates airflow values from the 30 data points defined in the transfer function.
In short, "calibrated" MAFs are mostly useless and one of the first things I tell people to get rid of when doing serious tuning.
If the Granatelli MAF you have acquired was intended to be used on a '96 GT then it will have been "calibrated" to work with 24lb/h injectors and an unmodified '96 GT tune. The calibration part is that the MAFs output curve has been adjusted to trick the unmodified tune into believing that less air is flowing than really is.
I.e. the calibrated MAF is a kludge left over from years ago when tunes could not be easily (or at all) modified, and when engine modifications required more air than the stock MAF could flow (it was "pegged") and more fuel at WOT.
The tune doesn't know that larger injectors have been installed, so it calculates a shorter injector pulse because of the MAF's lie. A shorter pulse with larger injectors = the proper amount of fuel. As air flow increases the MAF lies less and less, and the PCM starts to calculate "normal" pulse widths which with the larger injectors (larger than the tune thinks they are) deliver more fuel.
To use that MAF with your car you will need to determine its real transfer function, and load that into your tune, and then probably tweak it quite a bit because the shape of the "calibrated" MAF's transfer curve will be quite different from that of a non-calibrated MAF's curve; which is what the tune expects when it interpolates airflow values from the 30 data points defined in the transfer function.
In short, "calibrated" MAFs are mostly useless and one of the first things I tell people to get rid of when doing serious tuning.
11-24-2010, 09:38 AM
#4
3rd Gear Member
Thread Starter
Join Date: May 2007
Location: OH
Posts: 564
Well, I am not sure yet if the MAF is pegged or not. I wanted to take it to the dyno a month ago and do some logging but could never find the time. I just figured since I had the MAF, I would throw it on but thought I would ask first as I am not the type of person to just throw crap at my car 
.
It runs great now, seems down a little on power running 10psi which is why I thought the MAF and TB may be holding me back.
Thanks for the great descriptions on who that stuff works. I hope to someday actually understand all of that info.
.It runs great now, seems down a little on power running 10psi which is why I thought the MAF and TB may be holding me back.
Thanks for the great descriptions on who that stuff works. I hope to someday actually understand all of that info
.
11-24-2010, 10:16 AM
#5
5th Gear Member
Join Date: Nov 2005
Location: MN
Posts: 4,412
As Moose said, a "calibrated" MAF is not calibrated to just a specific injector capacity--but rather to a specific injector capacity AND a specific tune's MAF Transfer Function (MTF).
If the Granatelli MAF you have acquired was intended to be used on a '96 GT then it will have been "calibrated" to work with 24lb/h injectors and an unmodified '96 GT tune. The calibration part is that the MAFs output curve has been adjusted to trick the unmodified tune into believing that less air is flowing than really is.
I.e. the calibrated MAF is a kludge left over from years ago when tunes could not be easily (or at all) modified, and when engine modifications required more air than the stock MAF could flow (it was "pegged") and more fuel at WOT.
The tune doesn't know that larger injectors have been installed, so it calculates a shorter injector pulse because of the MAF's lie. A shorter pulse with larger injectors = the proper amount of fuel. As air flow increases the MAF lies less and less, and the PCM starts to calculate "normal" pulse widths which with the larger injectors (larger than the tune thinks they are) deliver more fuel.
To use that MAF with your car you will need to determine its real transfer function, and load that into your tune, and then probably tweak it quite a bit because the shape of the "calibrated" MAF's transfer curve will be quite different from that of a non-calibrated MAF's curve; which is what the tune expects when it interpolates airflow values from the 30 data points defined in the transfer function.
In short, "calibrated" MAFs are mostly useless and one of the first things I tell people to get rid of when doing serious tuning.
If the Granatelli MAF you have acquired was intended to be used on a '96 GT then it will have been "calibrated" to work with 24lb/h injectors and an unmodified '96 GT tune. The calibration part is that the MAFs output curve has been adjusted to trick the unmodified tune into believing that less air is flowing than really is.
I.e. the calibrated MAF is a kludge left over from years ago when tunes could not be easily (or at all) modified, and when engine modifications required more air than the stock MAF could flow (it was "pegged") and more fuel at WOT.
The tune doesn't know that larger injectors have been installed, so it calculates a shorter injector pulse because of the MAF's lie. A shorter pulse with larger injectors = the proper amount of fuel. As air flow increases the MAF lies less and less, and the PCM starts to calculate "normal" pulse widths which with the larger injectors (larger than the tune thinks they are) deliver more fuel.
To use that MAF with your car you will need to determine its real transfer function, and load that into your tune, and then probably tweak it quite a bit because the shape of the "calibrated" MAF's transfer curve will be quite different from that of a non-calibrated MAF's curve; which is what the tune expects when it interpolates airflow values from the 30 data points defined in the transfer function.
In short, "calibrated" MAFs are mostly useless and one of the first things I tell people to get rid of when doing serious tuning.
You take that information and compare your LTFT at a given MAF voltage and either subtract or add to your LTFT percentage depending if your whether your car is adding or subtracting fuel at those given MAF voltages ranges. Obviously attempting to zero in your LTFT.
11-24-2010, 06:41 PM
#6
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
I've never played around with sniper or tried to tune a mustang... but in the mazda world there is a pretty basic way to calibrate your MAF. You basically log your LTFT, MAF volts and MAF g/s. You start the log at idle still and slow bring the car up through the rpms range and monitor until you reach over 130 g/s. (best to do this a few times, and average the results)
You take that information and compare your LTFT at a given MAF voltage and either subtract or add to your LTFT percentage depending if your whether your car is adding or subtracting fuel at those given MAF voltages ranges. Obviously attempting to zero in your LTFT.
You take that information and compare your LTFT at a given MAF voltage and either subtract or add to your LTFT percentage depending if your whether your car is adding or subtracting fuel at those given MAF voltages ranges. Obviously attempting to zero in your LTFT.
Load is used for timing calculations and other control functions--this is also why so-called "calibrated" MAFs suck. The load will be calculated to be lower than it really is, and timing will be advanced more because of the low load.
This can be bad (think "holes in pistons bad")...
Last edited by cliffyk; 11-24-2010 at 06:48 PM.
11-26-2010, 09:13 AM
#8
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
It's a "variable" MAF calibrator, another kludge left over from when it was not possible to easily alter the tune, and which brings with it the same issues as calibrated MAFs as described above.
If you need a higher capacity MAF (which is ONLY needed if the one your have is close to pegging), then just buy one and adjust the tune's MAF transfer function to accommodate it.
If you need a higher capacity MAF (which is ONLY needed if the one your have is close to pegging), then just buy one and adjust the tune's MAF transfer function to accommodate it.
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