2 Bar E38 tuning with the MAF..

[Redline Motorsports]

If this is what we think the "calculation" for VE is;

VE = Constant + KMap².MAP² + KMap.MAP + KMapRPM.MAP.RPM + KRpm².RPM² + KRpm.RPM

where:
- Kxxx is the coefficient from the current zone
- MAP² is MAP squared
- MAP is MAP
- RPM is RPM
- RPM² is RPM squared

Then shouldn't a 2 Bar Map sensor (scaled), continue to provide additional fueling even after a MAF is maxed? It seems as if the MAP is used quite extensively in the calc and increasing the "KPA" value should make the final VE sum larger and hence more fueling. It is also my understanding that even though the MAF can max at a given grams/sec that it still continues to produce a hertz frequency that is still looked at by the PCM. Any thoughts?

[redhardsupra]

yes, because it's dynamically generated, it shouldnt have a limit on max airflow--aint it cool? :)
oh wait, you said MAF not SD, i saw the new response surface equations and jumped to conclusions...ehh, well in the end, MAF is still a lookup table, thus the number of bits assigned to store the lookup MAF flow numbers dictates the range and the resolution of the table. if they still got the stupid 512g/sec limit, then you're still screwed for higher flowing applications.

[Redline Motorsports]

I guess its qausi SD mode with MAF control! You'd have to think with GM's future plans of boosted GEN4 motors that this should be almost plug and play.

Would be nice to log boost pressure as well.

[Redline Motorsports]

Just came in from logging more data with my ProCharged Z. Since I am maxing the MAF it is obviously why the PCM keeps pushing PE towards the leaner side of the commanded AFR. How is the MAF Hrtz and or grams/cyl tied into the calculation? Is is used pre calculation and then used under another factor in that calc?

I really think that the addition of the 2 BAR map sensor will help offset the maxing, which is reducing fuel, and help to add fuel since it is raising a factor in the formula. Right now I am commanded bogus values just to stay rich enough into boost pressure.

This maxing also alters the way you make changes to the spark table since reported load goes backwards when the MAF maxes. Wish we could get a patch to move the MAF another 3000 hrtz....


Howard

[GMPX]

Actually, not sure on the Corvette but on the Holden putting a 2bar sensor on without altering the VE terms is BAD!.
The way the VE terms have been set up these things go very lean and throw heaps of timing in under boost.
Look the the graph of the calculated VE on a Holden.....
From about 2000 RPM up under boost the VE numbers reduce as MAP increases. (RPM in blue, MAP in red).
The Z06 VE at least does not take a dive under boost even if it does look a little odd. But keep in mind, GM's calculations were only taking in to account it was not going to be going above 105kPa.

The MAF limits I suspect will be hardware limitations in the ECM or the MAF itself. Remember GM already has boosted engines with these ECM's (The E67) - The Caddy Northstar in the STS-V as an example.

Cheers,
Ross

[redhardsupra]

Ross, how would changing MAP (assuming you'd change the volts to MAP values transfer function) screw with the new airflow generation model? unless the model really works with the rea MAP voltage readings, shouldn't it be the same? or is this more of a case where the new model is so sensitive to changes that 0.5-4.5v describing 0-105kpa vs 0.6-4.6v describing 15-210kpa would throw off the math?
I'm thinking it's the latter, considering the arbitrary, parametric nature of the new calcluations. any insights from oogling the code inside pcms?

[GMPX]

Because the real MAP value is a variable in the calculations (kPa, not sensor voltage) it alters the final calculated figure.
Problem is if in non boosted form they needed to taper off the VE value at say 98 - 102kPa for a given RPM range, as the MAP continues to increase (say between 105 and 190kPa) the taper will continue to decrease the calculated value because that is the 'curve' of that particular term.

Cheers,
Ross

[redhardsupra]

yea i obvieously know MAP is involved in the calcs, but if you get a different MAP in there and remap it properly, then no matter what the new voltage for let's say 80kPa was, it's still gonna be reported 80kPa, even though it shows up at a different voltage.

what do you mean by 'taper off VE?' i thought the whole idea of the new VE calcs is not to have any artificial limits.

obvieously, for the zones touching 105kPa, if you use the same equation to calculate ve at let's say 150kpa it's gonna be off, becuase it was not calibrated for it, so we just recalibrate it and v'oile, right?

any chance of having more 'zones' in COS for E38 in the future? (just please dont delay BB logging for the sake of this one ;) )

[GMPX]

yea i obvieously know MAP is involved in the calcs, but if you get a different MAP in there and remap it properly, then no matter what the new voltage for let's say 80kPa was, it's still gonna be reported 80kPa, even though it shows up at a different voltage.

I don't quite follow, though, it sounds like a band-aid fix to me ?



what do you mean by 'taper off VE?' i thought the whole idea of the new VE calcs is not to have any artificial limits.

It does have limits, think back to the old VE tables, you could get one cell and modify it's value. Not possible in the new system to narrow it down to a specific RPM-MAP cell. Though there is compromises in the real world these should not be an issue.



obvieously, for the zones touching 105kPa, if you use the same equation to calculate ve at let's say 150kpa it's gonna be off, becuase it was not calibrated for it, so we just recalibrate it and v'oile, right?

Yes. Change the term that cause the wrong trend of the graph.



any chance of having more 'zones' in COS for E38 in the future? (just please dont delay BB logging for the sake of this one ;) )

Ah, no that won't happen. What you could do is simply change the zoning so you have more control over area's that are more important.

Cheers,
Ross