In a message dated 3/20/2011 9:38:38 P.M. Eastern Daylight Time,
msteitle@gmail.com writes:
Bill,
The DNA (Dynamic Noise Attenuation) muffler is the only one I've used
that has not self-destructed in a matter of hours, except for the tangential
muffler which was too restrictive and caused other problems and gave poor
performance. (I should have listened to Lynn.) The DNA is not as
quiet as other mufflers, but it has worked for about 100 hours so far with no
sign of fatigue. Also, it has no packing to blow/burn out. ANR
headsets are a given.
Mark
The first outing of one of my Rotaries involved a tow to south Florida with
a tube frame first gen body. At Sebring the driver came in saying it won't pull
over 7,000 RPM. It would free rev to 9,000 RPM but not with a load on it. We
checked compression and it was fine (Usually means all is well) plus hot start
was instantly so again all is well. It turned out that we were right on best
power tune ( nearly highest EGT) and melted the new Flowmaster muffler designed
for the 427 Ford engine. All of the partitions were piled up at the exit
blocking the outlet nearly 100%. The engine sounded great and ran fine, but had
no power. This all happened in one lap. So the exit went from partially blocked
and still running OK, to blocked just a bit more, and running so poorly that
even the driver noticed it. So, I deduce that the range of blockage percentagees
is very small from unnoticed to not flying is, or can be very small.
Since the loss of power is from exhaust gas dilution of the incoming
charge, and at higher back pressure settings from displaced intake charge, from
excessive exhaust gasses still present when the intake port opens, that the
engine begins to loose effective displacement.
So the power loss may not involve a sudden change in output until the
blockage has been present for some time. Then the one piece that changes the
blockage by a few percent, is the last thing you notice first.
It is possible that reducing throttle slightly may get back some lost
power, as the intake length tune changes slightly and reduced flow lowers back
pressure. But that is a guess.
Lynn E. Hanover