Gen V VVE Value Calculation with Air Temp Correction

[travislambert]

Does someone know the precise formulas to work backwards to arrive at a Gen V VVE value without using a logged Volumetric Efficiency value? I've been using something that's close, but it's certainly not perfect. I thought I would reach out to see if anyone might help to refine the calculation.

Below is a snippet of Java code I've been using to experiment with known values.

Please assume a fixed camshaft at angle 0.0.

(For context, I'm fully aware of filtering transient data, how to calculate the error and adjust, etc. I'm not looking for anything using fuel trims, wideband readings, etc. I'm specifically looking for insight into the formulas to work backwards when the correct airflow and the conditions surrounding it are known.)

// Sample snapshot of known values
double mapKpa = 43.0;
double baroKpa = 97.0;
double airmassGramsPerSec = 6.5;
double intakeAirTempC = 36; // ~97F
double manifoldAirTempC = 47; // ~117F
double rpm = 660;
                
// Values calculated from known values
double mapMpa = mapKpa / 1000.0;
double pressureRatio = mapKpa / baroKpa; // 0.443
double manifoldAirTempKelvin = manifoldAirTempC + 273.15; // ~320
double revSec = rpm / 60.0; // 11
double cylinderIntakesPerRev = 4.0; // V8 4-Stroke Engine
double cylinderIntakesPerSec = revSec * cylinderIntakesPerRev; // 44
double cylAirmassGrams = airmassGramsPerSec / cylinderIntakesPerSec; // 0.1477 (This calculation checks out with logged value)
                
// This formula is close, but I'm not sure exactly how it's defined on a GEN 5 LT Engine
// I expected pressureRatio to be part of the equation, but I could never get it to work out.
double gmVe = ((cylAirmassGrams * manifoldAirTempKelvin) / mapMpa);

// This is where things get really fuzzy.
// I assume this air temp correction exists in some form based on what's in the tune.
// However, I don't know exactly how it works and whether it's based on ambient temp, intake temp, manifold temp, etc
// This is all made up.
double veBaseTempC = 20.0; // From tune
double veDeltaPerDegree = 0.00225;  // Completely made up value based on what appears to kind of work
double airTempDeltaC =  intakeAirTempC - veBaseTempC ;

// Final result
double gmVeCorrected = gmVe * (1.0 - (airTempDeltaC * veDeltaPerDegree));

[GHuggins]

Same math formulas work in genV's as gen4's. They're never perfect.

This is what I use - Cyl airmass - (([50041.223]*(273.15+[50011.241]) * (1000/[50030.91])) - this one gets it close
I also use ve error to maf + trim corrections - 100 * ([50040.71] - [2311.71]) / [2311.71] + ([50114.156] + [50116.156]) - this one is hit and miss

What I find is just how it's logged makes the most difference. Easy steady slow throttle with a trailer or something hooked up does the best for remote logging.

Then for whatever reason here lately I've found I have to move the formula's around to get them to log correctly - like something is wrong with the scanner. By this lets take the above for example - instead of this - 100 * ([50040.71] - [2311.71]) / [2311.71] + ([50114.156] + [50116.156]) I have to change it to this to get it to work - ((([50040.71] - [2311.71]) / [2311.71]) * 100) + ([50114.156] + [50116.156]) Something about the multiplication being first throws it off. It's best when you can to just fail the MAF and log the old way.

[travislambert]

Thank you.

Your first formula is equivalent to my "gmVe" calculation, and yeah, it certainly gets close most of the time. I was hoping that someone might know the secret to the last little bit of refinement. I believe it's in the final temperature correction because the VE within the tune is calibrated around a base temperature (also configurable). I suppose one could simply adjust this temperature value, but I'm trying to learn how to apply the reverse correction for that last bit of precision.

For what I'm working on the trim corrections aren't a factor. My calculations are working backwards under the assumption that the correct cylinder airmass is known.

[GHuggins]

If you're talking about the auto part in genV's just set it to what was logged for the errors or rather the new log. This is what I always do. I will say for whatever reason logs taken at colder temps seem to stay more in line with the auto correction formula built into the calibration.

The only way I know of that you could apply a correction around the built in temp correction is to first pull that code out of the calibration and reverse things from there.

[Alvin]

Does someone know the precise formulas to work backwards to arrive at a Gen V VVE value without using a logged Volumetric Efficiency value? I've been using something that's close, but it's certainly not perfect. I thought I would reach out to see if anyone might help to refine the calculation.

Below is a snippet of Java code I've been using to experiment with known values.

Please assume a fixed camshaft at angle 0.0.

(For context, I'm fully aware of filtering transient data, how to calculate the error and adjust, etc. I'm not looking for anything using fuel trims, wideband readings, etc. I'm specifically looking for insight into the formulas to work backwards when the correct airflow and the conditions surrounding it are known.)

// Sample snapshot of known values
double mapKpa = 43.0;
double baroKpa = 97.0;
double airmassGramsPerSec = 6.5;
double intakeAirTempC = 36; // ~97F
double manifoldAirTempC = 47; // ~117F
double rpm = 660;
                
// Values calculated from known values
double mapMpa = mapKpa / 1000.0;
double pressureRatio = mapKpa / baroKpa; // 0.443
double manifoldAirTempKelvin = manifoldAirTempC + 273.15; // ~320
double revSec = rpm / 60.0; // 11
double cylinderIntakesPerRev = 4.0; // V8 4-Stroke Engine
double cylinderIntakesPerSec = revSec * cylinderIntakesPerRev; // 44
double cylAirmassGrams = airmassGramsPerSec / cylinderIntakesPerSec; // 0.1477 (This calculation checks out with logged value)
                
// This formula is close, but I'm not sure exactly how it's defined on a GEN 5 LT Engine
// I expected pressureRatio to be part of the equation, but I could never get it to work out.
double gmVe = ((cylAirmassGrams * manifoldAirTempKelvin) / mapMpa);

// This is where things get really fuzzy.
// I assume this air temp correction exists in some form based on what's in the tune.
// However, I don't know exactly how it works and whether it's based on ambient temp, intake temp, manifold temp, etc
// This is all made up.
double veBaseTempC = 20.0; // From tune
double veDeltaPerDegree = 0.00225;  // Completely made up value based on what appears to kind of work
double airTempDeltaC =  intakeAirTempC - veBaseTempC ;

// Final result
double gmVeCorrected = gmVe * (1.0 - (airTempDeltaC * veDeltaPerDegree));

Are you trying to figure out what the manifold temp is? As in what temp is used for VVE? Or are you looking for like a density correction to airmass from temp?

What platform are you looking at?

I don't think enough people know on LT4's there is a PID/Channel Intake air temp sensor 3 bank one or something along those lines that spits out raw post supercharger IAT.

[travislambert]

Are you trying to figure out what the manifold temp is? As in what temp is used for VVE? Or are you looking for like a density correction to airmass from temp?

What platform are you looking at?

I don't think enough people know on LT4's there is a PID/Channel Intake air temp sensor 3 bank one or something along those lines that spits out raw post supercharger IAT.

Hi Alvin,

Thank you.

Are you trying to figure out what the manifold temp is? As in what temp is used for VVE?
No, I have a good understanding of that.

Or are you looking for like a density correction to airmass from temp?
What I'm looking for is the temp correction applied by the ECM. When the ECM looks up the VVE value (calculates the VVE value from the coefficients), it's applying a temperature correction to that value based on the delta between some current temperature and the VVE base calibration temperature (in the tune). Primarily, I'd like the formula portion for that temperature correction.

What platform are you looking at?
I'm working with a 2023 Camaro SS LT1 at the moment, but what I'm asking about is more of a general question. I am aware of the IAT3, etc. on the LT4.

My question isn't related to how to tune or anything like that. I can get to the correct values like everyone else does it with a couple of iterations of error feedback from trims and the wideband. I'm working on a tool to take some of the work out of that process. To improve what I have, I need to have a better understanding of what the ECM does when the temperature is different from the VVE base calibration temperature.

[smokeshow]

If the temperature correction factor is enabled, then the nominal VE value is multiplied by the square root of the charge temperature divided by the VE calibration temperature. That is, VE_tcorr = VE_nom * (MAT/MAT_base)^0.5. This accounts for the effect that the temperature-dependent speed of sound has on manifold/port tuning characteristics.

[GHuggins]

If the temperature correction factor is enabled, then the nominal VE value is multiplied by the square root of the charge temperature divided by the VE calibration temperature. That is, VE_tcorr = VE_nom * (MAT/MAT_base)^0.5. This accounts for the effect that the temperature-dependent speed of sound has on manifold/port tuning characteristics.

Is it OK to just change the base temperature setting for the auto correction to what is logged ambient wise? This is what I've been doing and seems to work, so was just wondering. Or is it for some reason using the ambient when flashed as it's base setting - I assume not but always wondered since hotter temps seem to throw it off about 3% from the logged ambient. This seems to be from 28ish+ Celsius where I start noticing this difference.

[travislambert]

If the temperature correction factor is enabled, then the nominal VE value is multiplied by the square root of the charge temperature divided by the VE calibration temperature. That is, VE_tcorr = VE_nom * (MAT/MAT_base)^0.5. This accounts for the effect that the temperature-dependent speed of sound has on manifold/port tuning characteristics.

Thanks so much! This is exactly the type of answer I was looking for. However, the way I understand what you've written, the correction seems implausibly high.

For example,
MAT = 40C (about 104F)
MAT_base = 20C (about 68F) (I'm using the VE Base Temp in the tune. Maybe this is the incorrect value?)
MAT/MAT_base = 2.0
(2.0)^0.5 = ~1.41

A 41% increase in the uncorrected VE value seems high.

What am I missing?

[smokeshow]

Needs to be in kelvin.

[travislambert]

Thank you so much! I'm sorry. I should have figured that out.

I'm testing using known values and the addition of this temperature correction just cut the error in half. Can't thank you enough!

[GHuggins]

Thank you so much! I'm sorry. I should have figured that out.

I'm testing using known values and the addition of this temperature correction just cut the error in half. Can't thank you enough!

So if I understand you correctly you're using the calibrations base temp plus the formula then multiplying that against the cylinder airmass equation? Guess this would be better for logging the ones where you can't fail the MAF if it actually cuts the errors down.

[travislambert]

So if I understand you correctly you're using the calibrations base temp plus the formula then multiplying that against the cylinder airmass equation? Guess this would be better for logging the ones where you can't fail the MAF if it actually cuts the errors down.

I'm a software guy so I perfer to do calculations in my own software where I can analyze multiple logs at once and apply advanced filtering, curve fitting, etc.

What I am working on is a program that takes a known "correct" MAF configuration as well as a collection of data logs and generates a baseline VVE table. This program purposely ignores LTFT, wideband readings, even the air mass readings because the MAF configuration input is assumed to be correct. Even if the MAF configuration was incorrect at the time of logging, I recalculate from the MAF frequency to the correct mass airflow rate. From the logs, it only uses MAP, BARO, MAF HZ, RPM, Manifold Temp, Cam angle, and Engine coolant temp. By comparing the output of the software with a known correct VVE, I can know when the software is moving in the right direction. By knowing how the temperature correction works, this allows me to apply the inverse to correct the VVE back to the stored baseline temp. This is very helpful when you're working with multiple logs captured during various conditions.

I'm sure the actual complexity far exceeds that of the models I have, but the software seems to get pretty darn close. My next venture is to try to learn more about the Airflow->Dynamic->VE Correction Factor. I've had these values incorporated into my models before, but it actually seemed to make the accuracy worse. I need to figure that out.

[Cringer]

Ah GMVE! My old nemesis! I shall watch with great interest here.

[GHuggins]

I'm a software guy so I perfer to do calculations in my own software where I can analyze multiple logs at once and apply advanced filtering, curve fitting, etc.

What I am working on is a program that takes a known "correct" MAF configuration as well as a collection of data logs and generates a baseline VVE table. This program purposely ignores LTFT, wideband readings, even the air mass readings because the MAF configuration input is assumed to be correct. Even if the MAF configuration was incorrect at the time of logging, I recalculate from the MAF frequency to the correct mass airflow rate. From the logs, it only uses MAP, BARO, MAF HZ, RPM, Manifold Temp, Cam angle, and Engine coolant temp. By comparing the output of the software with a known correct VVE, I can know when the software is moving in the right direction. By knowing how the temperature correction works, this allows me to apply the inverse to correct the VVE back to the stored baseline temp. This is very helpful when you're working with multiple logs captured during various conditions.

I'm sure the actual complexity far exceeds that of the models I have, but the software seems to get pretty darn close. My next venture is to try to learn more about the Airflow->Dynamic->VE Correction Factor. I've had these values incorporated into my models before, but it actually seemed to make the accuracy worse. I need to figure that out.

So I've discovered something as of late and I'm just wondering if your correction formula is doing the same thing as it is correcting for temps although I imagine it's still got the same problem I've run into, but maybe not?

OK, so I always thought VE Base Temp was the temp at which the logs were being taken. Worked good in the summer when temps weren't swinging that much and the previous winters weren't really that cold or didn't have that much of a temperature swing like they are this year. What I found is that setting the base temp setting to the logs ambient wasn't working anymore. It might be good for a log or two but then I would get 10% errors out of the blue even though maybe that time I didn't change it... This got me to thinking, what if it's the temperature at which it's flashed?

Well, so far as long as my customers set the base temp to what ambient is showing before they flash the cal, fueling for VE corrections has been staying within 2 to 4 %. The best I've seen it with the temp swings.

Just wondering if your math formula is already encompassing this, because it would be nice to not have to worry about the temp getting set every flash.

[TriPinTaZ]

Hot damn what a thread to wake up to today. I use a few different methods to tune VVE but I'm certainly interested in trying out another way.

[bk2life]

but I'm certainly interested in trying out another way.

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