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Mike,
I have the same phenomenon going on at ¾ throttle.
Tracy once
suggested that there may be more restriction somewhere other than the throttle body.
Thinking about this, I am using a modified stock Renesis intake. The stock
runners are about 1 inch in diameter and the throttle body is same as the stock
3 inches. So I have about 4 square inches in the runners, but over 6 square
inches (depending on the blockage of the butterfly with it wide open) in the
throttle body. This may be what is happening, but the dimensions are the same
as the stock engine and I have not heard of this complaint about the car. There
is a tube that bypasses the throttle body and injects air into the primary
ports on the car and I am not doing this on my engine. I read manifold
pressure at the back of the plenum and get 29-30 inches there. I need to read
the pressure at the entrance to the ports to see what I am losing in my
manifold. That may explain it?? I plan to also try the bypass to see if that
helps the idle as well.
Bill B
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Mike Wills
Sent: Sunday, September 06, 2009
11:18 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: DNA
muffler
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.
----- Original Message -----
Sent: Sunday, September
06, 2009 5:55 AM
Subject: [FlyRotary] Re:
DNA muffler
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.
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.
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