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Hi George,
I'll give it a shot. The Ec2 basically determines
how much fuel to inject using two factors - MAP (Manifold Absolute Pressure) and
OAT which basically tells it how dense the air is that the engine is ingesting
from the manifold. The Ec2 then examines its memory settings (a
different Map - read further)programmed in its memory (which you can
adjust with a mixture knob) for that manifold pressure match. Since the
manifold pressure can vary from apporx 12" Hg to 30"Hg (non-turbo), there are a
series of memory locations generally also referred to as the MAP (MAP in this
case referring to a topological chart) of the fuel settings. If you plot the
fuel mixture settings against RPM and Pressure it looks like a 2 dim
map). So once it matches the manifold pressure it senses through
the manifold pressure sensors with the corresponding memory location it extracts
the injector timing for that MAP and sends it on to the injectors (with
corrections for air temp).
The injectors fire once per revolution of the E shaft
(which corresponds to one face of an rotor, therefore, the faster the rpm the
more frequently the injectors fire. But, it basically provides the same
amount of fuel per revolution per specific manifold pressure (which of course is
controlled by the throttle setting and engine rpm) perhaps adjusted for Ve and
OAT.
Manifold Absolute Pressure is also one parameter to
determine how well you induction system is working. At sea level the MAP
is 29.92" Hg. So when you open your throttle wide open, you would like to
see 29.92" Hg on the gauge. If you do not and see less than 29.92"Hg (at
sea level) then that implies there is a restriction in your intake and a
resulting pressure loss. Less pressure means less dense air in the
manifold which means less fuel can be burnt which means less power.
That is the reason Rusty is concerned about whether the
MAP he is seeing really reflects what his engine is seeing or some fluke of
where the sensing port is in the intake. Generally you would like to have
less that 1/2" of a pressure drop any more than that (if its real) and you are
starting to loose power potential. So if the drop is real then Rusty
probably wants to modify his intake to eliminate it - if its just a fluke of
where he is sensing it - then he does not need to go to the trouble of designing
and fabricating a new intake.
That's my take on it. Hope it helps.
Ed
----- Original Message -----
Sent: Thursday, May 19, 2005 2:13
AM
Subject: [FlyRotary] Re: More MAP
measurement questions
Al,Rusty and All,
Excuse my ignorance here, I have absolutely no
knowledge about how ECU's work. I've heard people say that it reads MAP
settings - so what is a MAP, and if it's different because the pressure is
different at different places in the inlet, how can the computer calculate the
inlet charge and timing.
I'm confused!
George ( down under)
I'm working on a new theory
about my low MAP reading. The theory is that this isn't a problem at
all, but rather a difference in the way it's being measured.
What’s new about
this theory? This is what I was telling you a week or two ago.
J
I apologize for
lack of clarity, causing you to have to re-invent this
theory.
Al (Also running
TWM TB)
The TWM TB has a MAP port about
4 inches past the entrance of the TB throat. That means I'm
measuring the air pressure on the suction side of the largest restriction in
the system (from wide open space, to 41mm tube). Since there's
no significant restriction downstream from the TB, I would guess that I
could measure the MAP at the inlet of the side housing, and wouldn't
find it significantly lower than what I'm seeing in the TWM
TB. In other words, I'm measuring the worst possible MAP, which
is the suction side.
From what I understand, the
typical (if there is such a thing) intake has a large TB, feeding into an
open plenum, then into the smaller runners that go to the
engine. If I'm not mistaken, virtually everyone is measuring
their MAP in the open plenum, before the air has to enter the smaller
runners to go to the engine. In other words, the people
who are reading 30" are doing it on the pressure side of the largest
restriction.
I could babble on about this,
but my point is to ask where others are measuring their MAP (turbo folks
need not apply). You'll also have to give a general description of
your intake layout. I already know that Ed and Tracy are using
the "typical" situation. Is anyone measuring MAP in the runner to the
engine?
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