MAP and TPS LOAD based EFI

[Bob Wooten]

we use this differential pressure method @ work & this assumes critical
flow & the orifice diameter must remain constant.  we control the temp of
the orifice to maintain diameter so this is not an issue.  the problem is
that for the orifice to remain @ critical flow the pressure on one side of
the orifice must be greater than 2X the pressure on the other side (or vac
must be 1/2 the other side, perspective).  this would be impossible in a
motor that is going to go from total vac (10 KPA) to wide open (100 KPA), 
you would not be able to maintain critical flow.  

IMO, hot wire is the best bang for the buck for measuring mass flow.  as
for efficiency, I think that the best thing for what I think you are trying
to accomplish would be the run it & measure it method.  if it were easy to
do something that would not require map/air temp/hot wire/ etc the MFG
would have done it.  

if you want to go one level up on technology, i think that VW had it, w/a
variable pot connected to a vane in the intake tract.  this actually
compensates for both temp & pressure & VE, all @ the same time.  don't get
me wrong, it is not a great system, but it will work better than a straight
look up table, yet not as good as measuring these parameters & calculating
real time.


> [Original Message]
> From: John Dammeyer <johnd at autoartisans.com>
> To: <diy_efi at diy-efi.org>
> Date: 1/13/01 6:39:33 PM
> Subject: Re: MAP and TPS  LOAD based EFI
>
> Hi all,
> 
> In my opinion the answer is yes.
> 
> There are a number of methods for measuring gas flow.  Hot wire flow
meters
> that measure the cooling of an element in the gas stream.  Turbines.  A
> really neat one is to us an LDV;  Laser Doppler Velocimeter.  Another
method
> for measuring flow of gases in the oil industry is to use a differential
> pressure gauge and a restriction in the pipe.  If you know the diameter of
> the restriction and the temperature of the gas,  you can calculate the
flow
> rate from the difference in pressure.
> 
> The absolute pressure value inside the restriction isn't important;  it's
> the difference between the two.  Looking at an engine we see much the same
> problem.   What's really more important is how much air can we move into
the
> cylinder within the time that the intake valve is open.  If the pressure
> outside the intake manifold is half of sea level atmospheric -- say 15"
and
> the MAP sensor reads 15" at 70F then your airflow is 0 CFM.  In reality
the
> MAP will always read a little more vacuum than the ambient so it may ready
> 14.5" but in either case,  airflow is very slow.  Compare this to 29.92"
> atmospheric and 14.5" inside and you know you are sending air into the
> engine.
> 
> Now you can get away without a barometric pressure sensor and a 2D table
> RPM-MAP but it won't handle a trip to the mountains as well as one that
> corrects for altitude.
> 
> IMHO
> 
> Cheers,
> 
> John
> 
> 
> ----- Original Message -----
> From: "Tony Bryant" <brd at paradise.net.nz>
> To: <diy_efi at diy-efi.org>
> Sent: Saturday, January 13, 2001 5:48 PM
> Subject: Re: MAP and TPS LOAD based EFI
> 
> 
> > I have a question:
> >
> > Everybody knows that  as a first approximation a certain MAP & RPM will
> > give a constant fueling pulse length (assuming tempertature(s) are
> > constant).
> >
> > Everybody also knows that you need transient enrichment.
> >
> > Now the question is. Is it possible to get two steady state situations
in
> > which
> > the MAP, RPM, IAT are the same,but the air flow through the engine is
> > significantly different?
> >
> >
> >
> >
> >
> >
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> >
> 
>
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--- Bob Wooten
--- r71chevy at earthlink.net
--- www.r71camaro.homestead.com 


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