Calculating VE from MAF and MAP sensors

[Scot Sealander]

Chris Bennight wrote:
 
>    We have been talking about this on the LT1 edit mailing list, but
> thought I would ask you all to see what opinions you have, since
> there is probably much more experience here.
> 
>    On LT1's we have MAF and MAP sensors, and have been trying
> to use them to calculate a better VE for modified setups.
> 
>    Here is our logic -
> 
>   VE = actual airflow / theoretical airflow.


Here is part of a post from Feb 02, this year:

========================================================================
Here's a formula that should work:

        VE = m_dot / ( N * Vol * Rho / 120 ) * 100

where:          VE - volumetric efficiency (%)
                m_dot - mass air flow (g/s)
                N - crank speed (rpm)
                Vol - Engine Displacement (litres)
                Rho - Manifold Air Density (g/litre)

where:          Rho = 1.202 * MAP / 101.325
                MAP = Manifold Absolute Pressure (kPa)

You should also compensate the air density for temperature too since
the 1.202 is air density at 20_C and inlet temperature is elevated due
to heat transfer from the manifold surfaces etc.

Also VE for family cars these days will probably be better than 80%.
======================================================================

That was posted by Andrew Rabbitt from Orbital, a while ago.
Much simpler, and the variables are available in the ECM.  I worked
on this off and on for a while because I could not get a good
match with the table VE and MAF VE.  It takes a fair amount of
effort to get it to work right.

Where are you getting "T" (air temp) in your setup?  How accurate
do you think it is?  After taking 9 months or so to get the
variables right, my MAF VE and table VE usually match quite well
over the whole operating temp range.  And it is not over 80% VE, 
in my case.  Much closer to 65% max at 100 kPa MAP

I make the ECM calculate VE real time, then save it in added 
non-vol RAM.  It took a while, but the results are very
gratifying now.... ;-)

Scot Sealander
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