VE Formula Constants?

[Gelf VXR]

In the SAE.generic file we have the formula for VE

{SAE.MAF.gps}*({SAE.IAT.C}+273.15)/((displacement()*61.024)*{SAE.RPM}*{SAE.MAP.kPa})* 212544"

What do the two constant values 61.024 and 212544 represent?

[Gelf VXR]

61.024 is conversion factor from cc to ci

Which still leaves the constant 212544??

[Gelf VXR]

Found it, its "R" with in^3 as a unit.

[Gelf VXR]

I have derived from the B0200 calibration table showing separately VE & GMVE values, that for the E40 PCM, GM have used the value of 24.45071 for the molecular weight of the air, not 28.96 for dry air as shown in the SAE.generic file.

I assume they have they have lowered the value to account for humidity, for which water vapor has a molecular weight of 18.02.

If the relationship is linear when mixing the two gases, it equates to around 41% humidity


I wonder if they did the same for gas constant R? Again if the relationship is linear, 41% humidity would = 358.486, not 286.9 for dry air, as 461.5 is for water vapor.

[joecar]

I use this formula, VE per cylinder (for 8 cylinder engine):

VE[g*K/kPa] = {SAE.MAF.gps}*{CALC.DAT.K}/{SAE.MAP.kPa}/{SAE.RPM}*15

VE in g*K/kPa is not dependent on displacement (thus avoiding the cc/ci conversion), and is not dependent on the molecular mass of air (since it avoids displacement, i.e. no need to convert volume to mass).


The problem with molecular mass of air (and air density) is that it is not consistent day-to-day or geographically.

I am convinced that GM deals in VE in g*K/kPa (cylinder air mass normalized for temperature/pressure) and not %.

[Gelf VXR]

I have derived from the B0200 calibration table showing separately VE & GMVE values, that for the E40 PCM, GM have used the value of 24.45071 for the molecular weight of the air, not 28.96 for dry air as shown in the SAE.generic file.


I now know what i did wrong and its 28.96

VE*VOL/GMVE=R=28.964

when cylinder volume is enter as 708.191cc (should be 745.875cc for 5967cc LS2)

the error in the PCM calibration B0104 is screwing the VE table.

Edit: R in the above equation is wrong, it should be M, the molar mass of dry air

M = 28.964 = Air in the gas phase at standard temperature and pressure ( 1 atmosphere of pressure and 0°C.) has a mol of it (28.96 g) in 22.4 liters, coming to about 1.29 grams per liter.

[joecar]

VE [%] requires displacement, VE [g*K/kPa] is displacement free...

it seems to me that the V7 tunetool displays VE [%] by using B0104 and air density to calculate it, and it displays VE [g*K/kPa] directly without using B0104.

[Gelf VXR]

VE [%] requires displacement, VE [g*K/kPa] is displacement free...

it seems to me that the V7 tunetool displays VE [%] by using B0104 and air density to calculate it, and it displays VE [g*K/kPa] directly without using B0104.

Hi Joe

Its still wrong and should be corrected for anyone wanted to display %VE

I'm still trying to crack below pid return values which are way off the values in B0200, I thought the above might have been a contributing factor.

VE look up: E40.SCALEDCORVE_DMA

The search goes on, but this is interesting,

I'm looking at E37, E38, E38, E78 pids, and they all have this new pid

VE sum uncorrected: E##.SCALEDUNVE_DMA

Only the E38 has both, but its desription is a little more revealing

Map corrected VE: E38.SCALEDCORVE_DMA

It looks like the E40 was first with SCALEDCORVE, then E38 had both and subsequent s got PCM got SCALEDUNVE.

What does MAP corrected mean?? if I'm stuck with SCALEDCORVE, how is it calculated or can we get the SCALEDUNVE_DMA for the E40?

[joecar]

I now know what i did wrong and its 28.96

VE*VOL/GMVE=R=28.964

when cylinder volume is enter as 708.191cc (should be 745.875cc for 5967cc LS2)

the error in the PCM calibration B0104 is screwing the VE table.Hi Gelf,

Is the problem in B0104's value or in the tunetool using B0104 to calculate VE in %...?

Are you saying that the LS2 tune comes from the factory with the wrong value in B0104 (it should be 745 cc rather than 708 cc)...?

[Gelf VXR]

Hi Gelf,

Is the problem in B0104's value or in the tunetool using B0104 to calculate VE in %...?

Are you saying that the LS2 tune comes from the factory with the wrong value in B0104 (it should be 745 cc rather than 708 cc)...?

Hi Joe

Correct

[Gelf VXR]

What would be a MAP correcting factor?

[joecar]

Ok, I see...

My understanding is that the PCM does not use B0104 (it is for info)...

( change B0104 by a large amount and see if the engine runs )


the tunetool uses B0104 for displaying VE in % units;


you will have to correct B0104 yourself (or otherwise use g*K/kPa);


I don't think the tunetool should edit B0104 (what if someone sets it for their bored/stroked engine and have the sam VIN...?).

[Gelf VXR]

B0104 is not really my main concern for now, but it has been discussed elsewhere on this forum, resolving the difference between the GMVE value from the E40.SCALEDCORVE_DMA pid and the GMVE value calculated from the GM.APCYL_E40_DMA pid, which is close to B0200 table. A factor difference of around 1.4 variable not fixed?

What is the MAP correction as indicated in the E38 pid description?








Actually the SCALEDUNVE is a count value not g*K/kPa

[joecar]

I don't know how SCALEDUNVE works (I'll have to take a closer look at it), nor what MAP corrected means... swingtan/Simon would know.

[Gelf VXR]

Blacky kindly logged the E38.SCALEDCORVE pid, a few quick calculations show airflow from MAF, airmass g cyl DMA are all in agreement with this pid.

The E38.SCALEDUNVE follows closely to the E38.SCALEDCORVE pid, albeit a bit more erratic.

So whats going on with the E40? :wallbash:

its varying with a factor of 0.6 to 1.4 from B0200 table value

[Gelf VXR]

Seems like a MAF enabled issue

Log from ACLR8N with MAF enabled shows large discrepancy in cylinder air-mass values between MAF, DYNAIR, APCYL.DMA and the VE look-up SCALEDCORVE.DMA pid (see attached)

A log of mine some time back for Auto VE with MAF disabled shows DYNAIR, APCYL.DMA and SCALEDCORVE.DMA corresponding to one and other (see attached)