You can quiet it a bit with something like this. If it melts
 it is not likely to plug up the exhaust and cause a loss of power.
 Use about .090 or .125 thick 321 SS. 5 minutes at 4000 RPM oil
 temp 205 is not that bad. What kind of manifold pressure are you
 seeing at 4000 RPM?

 Paul Lamar

 Hi Mark,

looking at your exhaust, in my humble opinion, the exit from your
muffler or
expander, is way too big in cross section. For noise reduction, this
exit
should not be bigger but smaller then one exhaust pipe from the
engine. I do
not know how much smaller in your particular case.
On my single rotor, also PP port, the inlet into the expansion
chamber is 1
1/2" and the outlet is 1 1/8". I can stand next to the running
engine all
day long without a problem. Under certain condition, the prop noise
beats
the engine noise. My muffler is totally empty.
A couple of years ago we did a test at Tracy's test stand with a
resonator
chamber on one of his 13B engines. The resonator did not do very
much, but
when we put a 1 1/4 ID piece of pipe to the outlet, the subjective
judgement
of about 30 poeple was "wao it is quiet". The RPM loss with this ad-hoc
meassure was 200 at 6000 RPM.
I know it is not very scientific, however, even in cars, the larger tail
pipe makes a vehicle louder.
FWIW.

Richard Sohn
N2071U


No one would accuse our engine of being quiet in any way -- so this is
interesting to hear.  Paul, as I recall there was a specific reason for
the rectangular tube design -- can you refresh the whys & wherefores, or
was that a Jerry Hey inspiration?  Sure would be nice to have a much
smaller exit tube in any case.

If I were to change it, my instinct would be to cut the existing in half
length-wise & close it up again vs cutting it off and installing a round
exhaust tube.

Mark

We got some evidence from Russia of all places that square or rectangular
tubes were better than round. However the area of your is quite large.


Paul Lamar