Use of MAP in FI calcs

[Len Sabatine]

     Absolutly !!!!!!
     Len

>The lower the relative Baro, the more timing you can run, and help to
>recover some of that lose.
>If cuttin to the edge then even a tad leaner.
>(You only have to be as good as Jack Rouch (OK, (there are a few others)
>though to readem that well).
>Bruce
>
>
> >Ok, so baro is either sampled at power up or in some cases continuously
>sampled.  I agree with Ludis that what is needed particularly in the
>mass airflow calcs is the pressure inside the manifold, not outside.
>So.. is the only purpose for baro then the correction for the effect
>on exhaust scavenging that someone mentioned? I would think that a few
>kPa variation in baro would have minimal effect on scavenging.
>
>This is interesting; didya know that there are two separate and
>parallel threads on this very subject going on in efi332 and gmecm?
>Hee.
>
>Anyhoo, I doubt if it's strickly related to scavenging, which is a
>dynamic pressure effect that would be superimposed on the overall
>pumping pressures the engine is seeing. I'd bet it's just simply the
>issue of VE varying simply due to the inlet (i.e., intake) vrs outlet
>(exh) pressures, IOW the basic air pumping issue; the engine ingests
>air at a certain pressure, and expels it to ambient. MAP measures
>absolute ingestion pressure, but without BARO, you have to estimate
>the ambient pressure.
>
>Perhaps the best way to consider this whole thing is to think of
>variations in baro as equivalent to "a variation in total exhaust
>back-pressure with altitude", sotaspeak, since the pressure the
>exhaust dumps to (ambient) is changing with altitude. That way it's
>easy to see the relative effect of baro changes, and to also see that
>the VE tables can't take them into account like they do for whatever
>exhaust system you have on the vehicle when the engine is tuned (since
>the exhaust system if fixed, and hopefully doesn't change with
>altitude :).
>
>So merely from a pumping standpoint, you can see the effect of BARO.
>
>Gar
>
>
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