Air Load

[engineermike]

What is your opinion on the MAF location? Is in the intercooler better versus in the charge pipe? Do you think it makes a difference?

I don’t have direct experience with it in the charge pipe, so I don’t know how much large air density changes affects accuracy of the MAF element. The problem is if you simply calibrate the MAF based on fuel trims, but the calibration is dependent on the air density being relatively constant, then that’s bad. It also should be downstream of the BOV.

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[Jackson1320]

My kit comes from the procharger head unit and goes straight through the bov housing then into the intercooler and on the exit side of the intercooler is the m.a.f then exits the intercooler and then goes to the throttle body.
I have had the maf in the intercooler and in the pipe and both of the tunes provided have zero changes to the speed density part of the tune. It’s the same speed density calibration as stock. Should there be some changes

 

[engineermike]

No, the speed density model isn’t used in the air load calculation. The speed density model is there to determine what the manifold pressure is, since there is no MAP sensor, and manifold pressure is required to calculate throttle blade angle to achieve desired flow.

The whole thing works so inverted from what us old carburetor guys are used to and it really twists the noodle around. The calculations basically start with what’s desired to be in the cylinder and work their way out to what is required to achieve it.

 

[Jackson1320]

No, the speed density model isn’t used in the air load calculation. The speed density model is there to determine what the manifold pressure is, since there is no MAP sensor, and manifold pressure is required to calculate throttle blade angle to achieve desired flow.

The whole thing works so inverted from what us old carburetor guys are used to and it really twists the noodle around. The calculations basically start with what’s desired to be in the cylinder and work their way out to what is required to achieve it.

Ok so no matter where you install the maf the speed density does not change.
now if you change manifolds does your speed density needs to match the new manifold?

 

[engineermike]

…
now if you change manifolds does your speed density needs to match the new manifold?

The old SD modeling in the 80’s used MAP, IAT, speed, displacement, and a VE table to determine how much mass flow there is. The modern coyote SD model uses the same math to answer a different question: what must the MAP be at a known mass flow, IAT, speed, displacement, and VE?

The only part of that equation that isn’t measured or constant is the VE. The idea of swapping intake manifolds is usually to improve or change VE. Therefore, I believe the VE model would no longer be accurate if the manifold is changed. However, I’m not sure there’s a big enough difference when going from, say, a gen2 to a gen3 to take the time to correct it.

 

[markmurfie]

Don't forget SD can be used for filtering, anticipation, and plausibility to supplement the load from the MAF sensors untunable inaccuracies.

SD is an extremely forgiving calculation to error, but completely counter intuitive. You are not just going to guess as to wether a given airmass means more or less MAP. Then changing calculated MAP will change the injector flow rate, changing fuel trims. If that's how you got your MAF transfer, there's probably error in the transfer and error in your airmass value. With both coefficients and the x being unknown variables, it becomes nearly impossible to tune. With an external MAP sensor, barometric or throttle inlet pressure sensor, and a known good throttle body model, you can get an estimate mass airflow to tune the MAF transfer and SD too, but that's not something someone should plan on doing as a solution to poor modification choices.

A bench derived or equivalent MAF transfer, injector data, and MAP sensor are required for tuning speed density to any degree of accuracy. For tuning simplicity the calculated MAP error is best looked at as "close enough" and moved past.

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