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Mark/Ed/Bill,
I did not buy the same DNA that you bought. Mine is
a truck muffler with 2 1/4 inlets and outlets. I figured the larger body/volume
of the truck mufflers would help quiet things down. And the truck series
mufflers are almost identical in dimension to the muffler I started with. At
this point I'm hesitant to choke the thing down anymore by putting a reducer on
the outlet, but I guess there really isnt anything to loose. Except
HP.
I was thinking along the same lines as Bill - that
the DNA is more restrictive resulting in richer mixtures at equivalent MAP. My
home made muffler was a copy of the Moroso spiral flow mufflers, but with a
larger center tube. With my home made muffler I can look all the way through it
so the DNA is clearly more restrictive. Which is why I'm surprised it didnt work
better.
The DNA sure looks better than my home made
muffler. Weld quality is great. Time will tell how it holds up. The home made
muffler was Inconel so I expect it would be more durable in the long
run.
The point of something else in the airflow path
limiting HP is a good point. One of things I've noticed is that I reach max
power long before I reach max throttle. Since I'm making enough power for good
performance I wasnt too worried about this, but I am curious. Once I reach about
3/4 throttle I'm maxed out - the last 1/4 doesnt do anything.
Mike Wills
RV-4 N144MW
----- Original Message -----
Sent: Sunday, September 06, 2009 5:55
AM
Subject: [FlyRotary] Re: DNA
muffler
Mike,
I had the same impression of the DNA muffler. Then I remembered
what Tracy said about big pipes being louder than smaller pipes.
So, I ordered a tapered transition piece from Burns Stainless, bringing it
down from 3" to 2 1/4". That helped reduce the noise considerably
and I couldn't detect any reduction in hp. Or, you could spring for
a pair of those $800 headsets, or you could do both.
Mark S.
On Sat, Sep 5, 2009 at 10:46 PM, Mike Wills <rv-4mike@cox.net>
wrote:
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.
Mike Wills
RV-4
N144MW
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