More silly ideas

[Greg Hermann]

>Yep, in theory.  But, when you have Air Densities of 96% to 101% and the
>scanner shows the engine is at 98 K/Pa under both sets of conditions then
>there is a fly in the ointment.   Weither do to filtering,  the design of
>the sensor, or pulsation characteriestics, that the sensor is reading
>something is wrong.  Without an emission lab to do the research something
>needs done to compensate for it.   "My" baro/map idea isn't perfect, but
>it's a whole lot better than, being in error all the time, IMHO.....
>Grumpy

Coulpla things going on here, Grumps.

In flow of any fluid through any restriction or passage --pressure drop at
the same velocity is proportional to the _density_ of the fluid

--so with denser atmosphere, at WOT, same engine speed--there will be more
pressure drop going through the inlet tract and air filter and throttle
body, etc. to the location of the MAP sensor--a small, but _very_
significant difference that happens with changing BP.

--same kind of reasoning, exhaust back pressure against the engine will be
somewhat higher in proportion to everything else with ame operating
conditions, but denser atmosphere.

You're getting at some of the reasons why an engine's power loss at high
altitude is _not_exactly_ proportional to air density ratio change.

Regards, Greg
>
>
>| When you consider what the engine is doing, MAP makes a lot of sense since
>| what matters is the cylinder filling pressure which is maximum when MAP is
>| max. Secondly referncing to zero makes sense since the atmospheric
>pressure
>| is liable to vary all over the MAP and you do not want the same WOT
>setting
>| in Denver as in Miami. The zero reference point OTOH is the same no matter
>| where you are. Besides the engine does not care what the outside pressure
>| is, just what is in the manifold.
>|       A. Padgett Peterson, P.E. Cybernetic Psychophysicist