Idea for MAF calibration
02-06-2007, 12:01 PM
#1
Idea for MAF calibration Very Old School: multiply the MAF curve by a certain % until LTFT are where we want them to be.
Old School: re-design the MAF curve according to the LTFT vs. Frequency
New School: IFR definition according to fuel pressure and injectors flow, VE tuning, then reconnect the MAF then change the MAF curve...
Anyway: at the end the MAF is calibrated according to some kind of output: LTFT, STFT, Wideband and so on. But it's never a direct airflow measurement. It's the result of different mechanical and chemical influences.
Why not check the assembly using a real flowmeter? There are a lot of instruments for the industry that can give us a very accurate airflow.
Why not install filter, pipings, MAF and a flowmeter on a test device, apply vacuum behind the flowmeter (vacuumpump) and calibrate the MAF according to the flowmeter output?
...just an idea...
Old School: re-design the MAF curve according to the LTFT vs. Frequency
New School: IFR definition according to fuel pressure and injectors flow, VE tuning, then reconnect the MAF then change the MAF curve...
Anyway: at the end the MAF is calibrated according to some kind of output: LTFT, STFT, Wideband and so on. But it's never a direct airflow measurement. It's the result of different mechanical and chemical influences.
Why not check the assembly using a real flowmeter? There are a lot of instruments for the industry that can give us a very accurate airflow.
Why not install filter, pipings, MAF and a flowmeter on a test device, apply vacuum behind the flowmeter (vacuumpump) and calibrate the MAF according to the flowmeter output?
...just an idea...
02-06-2007, 01:10 PM
#2
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People (calibration labs) do this. I looked into it for
my own curiosity, but $500 worth of curious I was
not (setup & labor charges at a full service cal lab
with traceable calibrations for airflow, pressure and
frequency).
Now, you could also make yourself a few orifice
plates of known diameter, work with manometer
and ruler for pressure and first principles for flow
of an orifice, back-convert volume flow to mass flow
and (with a 1000CFM blower at your back) pull a
frequency & flow data set. This kind of project is
more up my alley ($) but low priority these days.
I don't like fixing an airflow error by overlaying a
fueling lie. Nor do I really like the idea of doing the
speed density tune and then making the MAF match
because most SD methods involve using trims or a
wideband, both of which are air -and- fuel involved
at the end of it. I would far prefer a MAF that was
dialed in from bottom to top (bottom particularly I
see a substantial error in what data I have, 2500Hz
with still air and the table says 5 g/sec mass flow
when I know for a fact it's zero) and then fix the
VE table so that dynamic airflow and MAF airflow are
matched up, and then figure out where any residual
AFR error comes from knowing the main air value is
for real.
my own curiosity, but $500 worth of curious I was
not (setup & labor charges at a full service cal lab
with traceable calibrations for airflow, pressure and
frequency).
Now, you could also make yourself a few orifice
plates of known diameter, work with manometer
and ruler for pressure and first principles for flow
of an orifice, back-convert volume flow to mass flow
and (with a 1000CFM blower at your back) pull a
frequency & flow data set. This kind of project is
more up my alley ($) but low priority these days.
I don't like fixing an airflow error by overlaying a
fueling lie. Nor do I really like the idea of doing the
speed density tune and then making the MAF match
because most SD methods involve using trims or a
wideband, both of which are air -and- fuel involved
at the end of it. I would far prefer a MAF that was
dialed in from bottom to top (bottom particularly I
see a substantial error in what data I have, 2500Hz
with still air and the table says 5 g/sec mass flow
when I know for a fact it's zero) and then fix the
VE table so that dynamic airflow and MAF airflow are
matched up, and then figure out where any residual
AFR error comes from knowing the main air value is
for real.
02-06-2007, 03:35 PM
#3
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Have you ever experienced a time where a tuned, calibrated MAF sensor was not accurate enough?
I havn't, and I doubt I ever will. Yes, it isn't perfect, but it's damn close considering any stock OBDII car will run a near perfect 13:1 AFR from idle to 500rpm shy of redline, where it dives slightly rich, usually to 12:1, but that's done on purpose.
The power you pick up from getting your AFR to 13.00:1 instead of 13:1 will be negligable.
I havn't, and I doubt I ever will. Yes, it isn't perfect, but it's damn close considering any stock OBDII car will run a near perfect 13:1 AFR from idle to 500rpm shy of redline, where it dives slightly rich, usually to 12:1, but that's done on purpose.
The power you pick up from getting your AFR to 13.00:1 instead of 13:1 will be negligable.
02-07-2007, 12:06 PM
#4
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Well, the as-delivered calibration of the stock MAF is
demonstrably off, at the low end. But this is dealt with
by the "blending" in the dynamic airflow so as not to
bother fueling much.
According to one of the cal labs I pinged at the time
thay had actually done batch testing of Delphi MAFs
before and seen about a 5% tolerance. Whether this
was +/-5% or a 5% total span, I did not ask.
My belief is that the MAF, unmolested / undamaged /
un-crusted-up is one of the more accurate sensors
we have, with the least external influences. But you
get down to cases, low RPM, reversion pulses, airflow
bias effects and it's a different matter. When operating
up in its sweet spot anyway, and provided a not-very-
turbulent, not-biased air stream to measure.
demonstrably off, at the low end. But this is dealt with
by the "blending" in the dynamic airflow so as not to
bother fueling much.
According to one of the cal labs I pinged at the time
thay had actually done batch testing of Delphi MAFs
before and seen about a 5% tolerance. Whether this
was +/-5% or a 5% total span, I did not ask.
My belief is that the MAF, unmolested / undamaged /
un-crusted-up is one of the more accurate sensors
we have, with the least external influences. But you
get down to cases, low RPM, reversion pulses, airflow
bias effects and it's a different matter. When operating
up in its sweet spot anyway, and provided a not-very-
turbulent, not-biased air stream to measure.
02-28-2007, 10:34 PM
#5
10 Second Club
I resisted modifying the MAF calibration curve for too long. I have gone over to the dark side because I want stock-style drivability and for my AFR to closely track the PE table at WOT. I have been unable to meet both requirements with a stock MAF calibration unless I fudge something else. SD/VE tuning is very easy. Start with a known-good fuel system - reasonably stable fuel pressure and flow-tested injectors. Then adjust the VE table using LTFTs below 4000 rpm and a wideband above. My motor is very happy with the resultant SD tune but adding the MAF with stock calibration spoils everything. With the MAF connected but disabled, if you log dynamic airflow and MAF frequency you see what SD mode estimates the MAF would say. Using Excel, you can then fit a third-order polynomial to the data and use the polynomial to generate new calibration points. The recalibrated MAF atop the SD tune works beautifully. I am somewhat dissatisfied with this method but not enough to try again soon to preserve the original MAF calibration. So, with reference to the original post, put me down as "New School".
Last edited by Gary Z; 03-01-2007 at 05:10 AM.
03-02-2007, 08:10 AM
#7
Your putting too much thought into this. Here is what i do with good results. (repeatable, and dyno proven)
Disable the VE portion of the tuning, go WOT at a low RPM (1200-1500) on teh dyno, and chart the commanded vs actual. Change the airflow values of the MAF to make the commanded = actual, and your good to go.
part throttle do by fuel trims (since that is what really matters anyway, if your running in closed loop normally)
I do not agree with some tuning company manufacturers that say do not adjust the maf curve.
Ryan
Disable the VE portion of the tuning, go WOT at a low RPM (1200-1500) on teh dyno, and chart the commanded vs actual. Change the airflow values of the MAF to make the commanded = actual, and your good to go.
part throttle do by fuel trims (since that is what really matters anyway, if your running in closed loop normally)
I do not agree with some tuning company manufacturers that say do not adjust the maf curve.
Ryan
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03-02-2007, 09:43 AM
#8
At the beginning I tried to adjust fuel trims by changing the MAF curve.
It works fine but that changed the calculated torque too, which influences the shift pressure (A4). I think it also changes the G/Cyl values which are used for the timing values.
I now prefer to change the IFR curve (logging for MAP, LTFT and STFT).
It's a very stable tune. During a year I saw corrections (LTFT) of only +/- 2%.
So I let the MAF alone.
It works fine but that changed the calculated torque too, which influences the shift pressure (A4). I think it also changes the G/Cyl values which are used for the timing values.
I now prefer to change the IFR curve (logging for MAP, LTFT and STFT).
It's a very stable tune. During a year I saw corrections (LTFT) of only +/- 2%.
So I let the MAF alone.
03-02-2007, 11:12 AM
#9
Actually if you go back to ls1.com and back in 2000 + 2001 they were fixing things via IFR. 'TheDragon' comes to mind as a huge proponent. Anyway, to me IFR is WAY old school.
Myself I left the MAF curve alone becasue of how much it can mess up ( as you pointed out ).
Myself I left the MAF curve alone becasue of how much it can mess up ( as you pointed out ).
03-04-2007, 04:45 PM
#11
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The only true way to calibrate it is with an external test stand...
The thing with HP Tuners is that you can trick the car into doing what you want 345345 different ways (so i exagerate..)
The thing with HP Tuners is that you can trick the car into doing what you want 345345 different ways (so i exagerate..)
03-04-2007, 04:59 PM
#12
Major OEM's (not sure about GM) flow them, with the entire intake system, from airfilter, to the TB, to get the correct transfer function for the maf.
Since the first thing anybody ever does it throw on a lid, this is altered from the first mod of these cars.
Ryan
Since the first thing anybody ever does it throw on a lid, this is altered from the first mod of these cars.
Ryan
