[Gmecm] MAF specs and MAP replacement.

[bcroe at juno.com]

Mole is just a number of molecules, equivalent 
to mass.  Just use a different constant R to make 
it work.  Bruce Roe

20 May 2005 Robert Fleming <robert.fleming at sbcglobal.net> writes:
> n is number of moles, not mass

> Robert
> 
> 
> --- Steve Ravet <Steve.Ravet at arm.com> wrote:
> 
> > The end goal of EFI is to inject the correct amount
> > of fuel for the mass
> > of air that is passing through the engine, to
> > produce the desired
> > air-fuel ratio.  So knowing the mass of air passing
> > through the engine
> > is the crucial bit of information.
> >  
> > MAF measures mass directly.  If you don't have MAF
> > then you have to
> > calculate mass.  Look up the ideal gas law, PV=nRT.
> >  
> > P=pressure
> > V=volume
> > n=mass
> > T=temperature
> > R=constant to make units work out correctly.
> >  
> > MAP gives you pressure.  Volume is calculated from
> > RPM.  T comes from
> > the inlet air temp sensor, or is just a constant. 
> > This calculation is
> > generally done beforehand and stored in the form of
> > a volumetric
> > efficiency table that is indexed via MAP and RPM.
> >  
> > So your box will have to take MAP and RPM as a
> > minimum, and will have to
> > have some constants related to the engine in there
> > also.  What's your
> > application?  I think most MAF systems fall back on
> > MAP in the case of a
> > defective MAF sensor, you can probably "convert" to
> > MAP by simply
> > unplugging the MAF.
> >  
> > --steve