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Date: Wed, 01 Sep 2004 13:47:58 -0400
From: Mike Robert <pmrobert@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] MAP filter
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Al Gietzen wrote:

>>
>
> Al, been there, doing that with the RC thing - .04"/1mm and a cheap
>
> generic plastic fuel filter work very well at all RPM and load ranges. I
>
> can send you some datalogs if you wish. If the orifice is too small, the
>
> ECU has to wait a few tenths of a second for an accurate MAP signal.
>
> This causes a short period of enleanment and a momentary stumble. It's
>
> actually the flow in and out of the capacitance that you're restricting,
>
> not the extremely miniscule flow that the sensor diaphragm generates, if
>
> any. I think most MAP sensors are strain gauges. You want
>
> Manifold->R->C->MAP sensor as your sequence of parts. I've spent many
>
> hours getting this right by trial and error and have extremely smooth
>
> sensor response even at .01 second data logging intervals at 800 rpm idle.
>
> -Mike
>
> 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?
>
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. 
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.


> Al
>
-Mike