VE Table units

[Chris@HPTuners]

Well, finally getting around to this...

The Main VE table calc works like this:

g/cyl * 8192 = MAP * 51.2 * VE / (T * 32)

note the T is in Kelvin and is a mix of IAT and ECT and incorporates various heating effects.

If you look at the gas laws you get PV = nRT, so in grams you get G = nM where M is 28.96 g/mol and R is 8.3145.

G (grams) = M * P * V / (R * T)

P = MAP x 51.2
T = T x 32
G is grams x 8192

substiuting these two you get:

VE = 8192 * 28.96 * 32 * V / (8.3145 * 51.2)

or

VE table value = 17833 * V

To get to VE % normalise to Cylinder Volume (0.708 L for an LS1). Giving:

VE% = VE value / (178.33 * CylVol)


Maybe we should rename this table

[Bink]

My head hurts!
Thank you for the info gameover ;D

g/cyl * 8192 = MAP * 51.2 * VE / (T * 32)



8192 - where is this from?

T * 32 - Does the PCM blend the IAT & ECT values?? Where does "32" come from?


VE = 8192 * 28.96 * 32 * V / (8.3145 * 51.2) - Where did T go??

joel

[Chris@HPTuners]

these are the internal factors for storage of the values inside the PCM.

ie. you can;t just store 0.1566 g/cyl inside the PCM as a hex number so you use some of the lower bits for your decimal. in this case 8192 means use the lower 13 bits for the decimal fraction... likewise for the other variables.

the other values cancel when you combine the two equations

[S2H]

so what is "V" ???


VE table value = 17833 * V

[Chris@HPTuners]

V = volume

[S2H]

cylinder volume?? engine volume??

just trying to get a better grasp on this...

[FastFieros]

SoundEngine

You should read this thread... http://www.ls1tech.com/forums/showthread.php?t=287094

Really packed full of info...

Of course, if you are working on a V6 PCM understanding vs the V8 understanding, note there are differences in the formula's.

Loyde

[S2H]

thats what got me looking here..LOL

[stocker2]

Chris, Did you take the equation 'g/cyl * 8192 = MAP * 51.2 * VE / (T * 32)' and divide by 5 for the colorado. Provided that MAP is in KPa, T is in Kelvin; I will get a value 0f 12200 for VE, using .60g/cyl, 88 KPa, 300K. If I divide by 5 i get 2094, which corresponds perfectly to present values for the engine.

Calibrating the VE tables for us is hard since most of the advice threads are for table that are strictly on a percentage base.

To calibrate my VE table do I take the calculated grams per cylinder adjust them to the fuel trim values? Say I'm running a consistent +5 combined short term and long term trim, do I multiply the g/cyl by 1.05 and throw that back into the VE equation and then reset the cell value for the particular cam angle it was at?

[redhardsupra]

Chris, could you take a look at something I've developed on my own:
http://www.allmod.net/hpt/HowSpeedDensityWorks.doc

I'm wondering how it all works into your math here

[Chris@HPTuners]

i just skimmed it but it looks reasonable. the PCM's MAP based airmass forumla on the LS1 is simple. we just display the units as a % of the theoretical maximum using cylinder volume as a guide. since most people back then wanted a % based VE instead of the g.K/kPa values. For the LS2 etc. we just show the g.K/kPa values becuase GM screwed up the cylinder volume on many of the early LS2's vehicles.

g/cyl = VE.MAP / Tk

where VE is g.K/kPa & Tk is the estimated charge temperature in degrees Kelvin.

No matter if you are working in % or g.K/kPa everything is linear so % AFR error measurements can be applied to provide the correct fueling adjustment.

Generally the biggest issue in GM's SD is estimating the aircharge temperature and is usually the reason for fueling errors. Also the lack of a reversion term for cammed cars contributes to the problem. As does the lack of a TPS based feedforward term for large throttle transients. But you can only work with what they give you.

Chris...