> > Ed, you might want to consider a round muffler made out of Inconel (or
heavt

SS)fed by both exhaust pipes with an exit pipe facing away from the

fuselage.

 ... SNIP....

If you've hard mounted your exhaust system to the fuselage that's a big

no-no

because it can lead to fatigue failures because the engine is

transmitting the

vibrations thru the exhaust pipes to the fuselage. If the system is

built well

you won't need a hard mount, or if necessary, brace it back to the

engine.

Chuck Harbert.

Allan Tolle in the Power Sport RV4 went 138 MPH in the Sun & Fun 100 mile

race

with two long pipes and they were not that noisy as I recall. I like

Finn's

idea of opening up the front of the large concentric tube to cool the guts
of the muffler. Should allow a lighter weight muffler.

Paul Lamar

Ed Anderson wrote:

Chuck,
    I agree that hard mounting the exhaust without some flex between it and
the headers is asking for fatigue failure.  I purposely left the joints
between header and mufflers on the loose side.  However, based on the
vibration transmitted into the cockpit, its clear that there was not
sufficient isolation.  I had intended to use rubber exhaust donuts to reduce
the vibration but did not. I am going to experiment with two 18" lengths of
0.035 SS with multiple holes drilled in the bottom half of the tube and the
end squeezed down to a fishtail 1/2" in width.  I don't expect it to be as
quite as the arrangement of a "Round" muffler under the cowl, but it will be
lighter.  A book on Exhaust and Intake systems indicate there is some merit
to this configuration, so I thought I would give it a try.

Ed Anderson

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