Well, I can always be wrong, Bill.
However, more air mass flow at the same rpm (due to “theoretical”
better flow, i.e. Better volumetric efficiency) would mean the EC2 would see
higher manifold pressure and should respond by enrichening the mixture to match
– I mean that is what the EC does- match fuel flow to manifold
pressure. Now you would think that if it matched the higher manifold
pressure accurately then while more fuel would be flowing – the air/fuel
ratio (which is what we are looking at on our indicator) should theoretically
remain the same. Could be the EC “over compensated” ?
Perhaps another way of looking at is with
the old muffler which gave a certain manifold pressure at rpm X would then
point to the corresponding manifold pressure bin in the EC2 MCT. Now if
at the same rpm with the new muffler the airflow mass flow is greater - then
the manifold pressure at X rpm will be corresponding greater. Since the
EC2/3 is using manifold pressure to point to the correct bin – it is now
pointing a couple of bins higher in the map. Normally the higher you are
in the map the more fuel is signaled to flow. So Mike would then have to “re-adjust”
the MCT table to match the new volumetric efficiency increase.
Now if the new muffler was producing more
back pressure then the airflow would be lower for the same RPM or the
Volumetric efficiency would be somewhat worst than the with the old
muffler. So if the lower air mass flow corresponds to a lower manifold
pressure then the EC2 should be point a couple of bins lower in the MCT which normally
would signal less fuel is required and injected to match the lower air flow.
Or at least that is my take on it.
Perhaps Tracy is loafing around today {:>) and
will come on line the real explanation.
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Bill Bradburry
Sent: Sunday, September 06, 2009
8:45 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: DNA
muffler
Ed,
We are on opposite sides of this possibility. Seems that if there
were more air allowed, the mixture would lean, not richen. This is
exactly what I was thinking when I suggested that the muffler might cause more
back pressure, lower the air flow, and cause richness.???
What I may be missing is just what the EC-2/3 would do if it saw a
certain condition. Explain, please.
Bill B
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Sunday, September 06, 2009
8:20 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: DNA
muffler
Hi Mike,
Interesting reaction of engine to your DNA
muffler. A possible explanation for richer across the board. It
appears that the DNA muffler may offer less back pressure to the engine meaning
you get more air into the engine at any given rpm. That could increase
your manifold pressure and drive the EC2 to enrichen the mixture to
compensate. The reason the top end rpm may not change is that at that
point there is some other restriction such as the intake, TB, etc that may come
into play. Just a theory of course.
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Mike Wills
Sent: Saturday, September 05, 2009
11:47 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] DNA muffler
Received my DNA muffler this past week and got it installed
and running. Havent flown it yet, but have done some taxi and full power
runups. So far I'm a little disappointed. It doesnt appear to be any quieter
than my home made muffler. I'll reserve judgement until I actually fly it, but
from the cockpit the noise level seems the same, and my buddy standing about 50
' away said he thought the noise level was the same.
One thing not the same - the muffler screwed up my
tuning. It appears to be considerably richer now all across the RPM range. And
the big bog at the staging point that took me so long to tune out is back with
a vengeance. Oddly, in spite of the tune issues it still appears to reach the
same static RPM as previously.
Looks like the solution for me is going to be the high
$ headset and the rest of the world is just going to have to live with it.
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