VE Table Editing

[Screamn03]

I would figure since this motor has a cam and other airflow enhancing modifications done to it that the VE table is the first table that should be edited. Am I correct on this? If I am anyone have a good procedure for this?

BTW-stock MAF is on the car right now in case you looked at my sig

[jimmyblue]

From what I've seen it's pretty much cut-and-try, and
most people just adjust as little as possible (down at
the low end, where VE value fidelity affects idle quality).

I believe you can use the MAF (if you trust its output)
to judge the speed-density valculation and VE; there
is a MAF = VE*MAP*RPM kind of equation that you'd
have to get scaled right for the units you can log, and
maybe use Excel to then look at 1-MAF/(VEMAPRPM) as
an error % or something like that. All falls apart once
you get away from the stocker, but as long as you have
that and are away from its lower and upper accuracy
limits that should be good. I think for the most part the
cam overlap only affects VE at the low end, shorty
headers are probably not affecting much except maybe
at the extreme top end though long tubes will extract
further down the band.

[Screamn03]

In short summary I ended up finding this formula to work the best because it's simple and I understand it:

%VE = (MAF * (IAT + 273.15) / (DISPL * RPM * MAP)) * 212544

I believe these to be the correct units:

MAF=grams/second
IAT=*C
DISP=One Cylinder in CU/IN
MAP=KPA

I've been searching on LS1Tech about this and started this thread that is a summary of the information that I found:
http://www.ls1tech.com/forums/showthread.php?t=156935



??? ??? ??? ??? ??? ??? ??? ??? ???

:huh2: :huh2: :huh2: :huh2:

[Chris@HPTuners]

you need to understand what VE is guys. VE is just the amount (volume) of air you are getting into each cylinder versus the amount you could theoretically get in there under ideal conditions. Hence the name *volumetric* efficiency.

So you get:

VE = CylAir Actual / CylAir Ideal

if you have a MAF and you trust its measurement then to work out the amount of air going into each cylinder on average for a V8 engine is just:

CylAir Actual = MAF(gm/sec) *15 / RPM

now to work out CylAir Ideal you need to go look at the gas equations PV = nRT and plug in the atmospheric (barometric) pressure for P, the cylinder volume for V, the Air Temperature (in Kelvin) for T and the values of R etc...

you get something like:

CylAir Ideal = (BARO * (Displ/8) * 28.96) / (8.3145 * (IAT + 273))

then divide the two values to get the VE or:

VE = (MAF(gm/sec) *15 / RPM) / ((BARO * (Displ/8) * 28.96) / (8.3145 * (IAT + 273)))

which reduces to your equation once you adjust for units etc.

If you put MAP in instead of BARO you will get the theoretical airmass at the current throttle position (ie. you are removing the effects of intake tract loss). True VE is compared against BARO.

[jimmyblue]

But the VE as used in our engine controls is
the MAP referenced one, yes?

[Chris@HPTuners]

But the VE as used in our engine controls is
the MAP referenced one, yes?

well, just remember that the VE table is there to tell the PCM how much air is in each cylinder at the current MAP/RPM when the MAF is not there. It's replacing the MAF measured part of the equation (ie. the actual CylAir).