Interesting P&H Driver Link and a MAP Question

[Bruce Plecan]

From: "Ken Bauman" <303print at northrim.net>
OK, I once thought I had it understood, but know I guess I don't. I'm
concerned
that a system be able to easily handle altitude changes such as the example
of
going up the mountain.

The oems, do enough to get by.
On some systems the do a baro calc, at certain heavy throttle conditions.

So am I to understand the systems that only use 1 pressure sensor (typical
GM
MAP) won't have good compensation for altitude changes? One of these mfg's
told
me their system reads map referenced to absolute pressure so it is not an
issue.

It is if you need 8% VE change for baro, in addition to what the engine
normally wants.   By the time you have a 15% VE change in one increment,
it's sloppy at best.

So Bruce can a system use only one sensor if it has more resolution? I'm
missing something, and now feel like I'm back in EFI 101. Would it be too
much
to ask for a good explanation of the meaning and relationship of MAP and
BARO
to EFI? Please explain.

You can do anything, it's a matter of how fine of point you want on your
pencil.
MAP is internal to the engine, BARO is external.
Full time BARO, is just like sampling times for Coolant temp, or MAT,  the
more timing the info., the best the fueling and timing calculations, now for
the biggy,  depending on what you see as necessary.  A mild street engine is
a far cry from what I want in a hipo engine.

The way I had it understood was that once the engine was pulling a vacuum
there
was no way to know what the outside pressure was. That was the reason for
the
second baro sensor. But obviously there is a direct connection to the
outside
(the butterfly) a person recently told me that the outside pressure effects
the
amount of vacuum pulled so a second sensor was not needed. So is it that we
need the second sensor because we don't have enough resolution to adequately
measure the effect outside pressure has on the vacuum? Or.???

With enough resolution the single MAP would be fine.  But, the table would
be huge.   By having an overall trim, we can cut that table size, alot.
IMHO, it's much easier to get the same net result with just using an extra
sensor.
Bruce


Ken Bauman

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