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Al, been there, doing that with the RC thing - .04"/1mm and a cheap
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generic plastic fuel filter work very well at all RPM and load ranges. I
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can send you some datalogs if you wish. If the orifice is too small, the
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ECU has to wait a few tenths of a second for an accurate MAP signal.
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This causes a short period of enleanment and a momentary stumble. It's
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actually the flow in and out of the capacitance that you're restricting,
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not the extremely miniscule flow that the sensor diaphragm generates, if
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any. I think most MAP sensors are strain gauges. You want
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Manifold->R->C->MAP sensor as your sequence of parts. I've spent many
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hours getting this right by trial and error and have extremely smooth
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sensor response even at .01 second data logging intervals at 800 rpm idle.
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-Mike
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Can’t argue with success. Yes, you would not want a
very small
restrictor upstream from the accumulator. My logic was
telling me that
the most effective pulse dampening with the least effect
on response
time would be a smaller restrictor on the controller
side. But logic
doesn’t always match reality, and I suppose that
option was one of
your trials.
What application and ECU are you using? Do you suppose it is
independent of those things?
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I'm
running a streetported 12A rotary in an '83 RX-7 using the
MegaSquirt
fuel only ECU, Weber Alpha 2x50mm bodies (very similar to the
TWM
bodies) w/ an approximately 19" tract from the rotor face in each
port
to the end of the TB intake bell. I'm no EE but from what I can
tell,
most pressure sensors up to the job of reporting MAP are pretty
much
the same as far as operating theory. A Motorola MPX4250 is the
sensor
used in my app. Another thing I'd like to mention is that I also
have
approximately 6' of 1/4" line from the manifold to the RC/MAP
sensor
combo so there's definitely some extra volume from the hose run.
This could be quite a
difference – ¼” i.d that long is about 3.5 cu. in. upstream from
the restrictor. How big is the filter?
I
believe that each application/install has it's variables and no one
solution
will be perfect for everybody though we can all learn from each
other. Well
said.
My setup had a short
run of about 3’ if 1/8” i.d. line, and the running was rough. So
far the best results I’ve had was on the first quick try where I teed
together the A & B controller lines with a 5/32 plastic T, then added in
about 18” of 5/16” i.d. vinyl tube from there to the sensor. The T
is a restrictor of sorts because it has an i.d. of about .065. So it was line,
restrictor, volume (approx. 1.4 cu in.). Unfortunately, the test was very
short because I was also measuring oil drain from the redrive, and the engine
had not warmed up. But I had about 15 seconds of completely smooth running at
1600 rpm before shutting down. I was thrilled because up that point I had
nothing but roughness.
I bought a small
plastic fuel filter, made an orifice in one end by filling the inlet with about
¾” of epoxy microglass, and drilling it out to .063 (smallest drill I
had). The filter has roughly 1 cu. in. of volume. I tried this in place of the
18” of vinyl tube with the orifice toward the manifold. This was better
than no filter, but still rough. I then reversed it placing the orifice on the
end toward the sensor. Seemed to run a little smoother, but at little lean of
optimum mixture it got into kind of a slow surging behavior which I had not experienced
before. Still no joy.
This may all be a bit
meaningless since during these runs the engine was warming up. When I went
back to the first 5/16” tube setup I could not get complete smoothness at
1600; maybe because this time the engine was warm.
It’s a guessing
game, and what is needed is an oscilloscope on the MAP sensor output.
Al