RE: MAF vs. AFM

[Ed Walters <EdW@xxxxxxxxx>]

Mark Kibort wrote:
You had a AFM first and then you converted to a MAF. How did you set up the
MAF to produce the same voltages out that the afm produced for equivilant
mass flow? (yes, the AFM is a very accurate , inefficient,  mass flow device
even though it is not called such)  so, Im interested as we have estimated a
1/2 psi to 3/4 psi pressure drop across the AFM and that would confim the
5-10 hp gain you saw.  However, if you used the same fuel mapping , how do
we know the differences were not due to mixture differences?

Courious to hear of how the conversion was done, and how the fuel mixture is
set up with the MAF system.

Mark Kibort
************
The stock AFM was sent out to the MAF meter manufacturer to be flow tested.
A 75mm MAF meter was recalibrated to match the AFM curve.  I do not know if
the calibration is accomplished entirely within the MAF or if there is
something (i.e. lookup table) in the attached black box where the trim pots
reside.  A MAF for a car using a different part # AFM would need a different
calibration.

I doubt the power gain is due to mixture changes.  The MAF was calibrated
specifically to my AFM.  Also, my car feels slightly flat at full throttle.
At 95% throttle, where the engine runs in closed loop, the car feels fine.
I probably need a few psi more fuel to compensate for the additional air
during open loop operation.  Even with this full throttle "softness", the
car still showed ten more HP on the G-Tech.

One more thing.... my car still suffers from the "torque hole" between 2500
and 3000 RPM.  This problem is addressed well by advancing timing.  A Jim C.
chip would suit me well.  I'm sure the 75 mm MAF isn't helping the
situation.  A 2 valve big six probably can't use anything more than a 60 to
65mm MAF.  Something to think about.

I thought an AFM was a device for measuring volume flow, not mass flow.
Although it is very accurate at lower flow rates, its divergant behavior
does not lend itself well to accurate high flow measurement.  Is this why
the Bosch ECU runs in open loop at full throttle?

Disclaimer:  I took one semester of automatic controls.  All statements made
by me are either uninformed opinions or wild guesses pulled out of my nether
regions.  I'm guessing here.  Some of the more knowledgable engine experts
may have a better idea of what's going on here.  I'm open to opinions.

Ed

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