Here's my new muffler parts. Inside pipe is 321 stainless, .035", outside tube is
 .030 304 stainless. There is another 17" of inside tube for a total of 52" of inside
 tube.
 Brian Trubee

 Looks good Brian. The inside pipe is pretty thin but if it fails there is unlikely to
 be a loss of power.

 Paul Lamar

 Brian,
 Are you sure you have enough holes in the inner pipe?

 Mark

 Are you joking? :) It's open on the far end.

 Paul Lamar

Yeah, so is a straight pipe, but it wouldn't quiet the rotary roar at all.

Mark

In theory this would. If one lowers the pressure and reduces the temperature in a
pipe the velocity will be reduced. The noise comes from the sudden expansion of hot,
high velocity, high pressure gases at the end of the pipe.

A gun silencer works in the same way.


"Boyle's law (sometimes referred to as the Boyle–Mariotte law) states that the
absolute pressure and volume of a given mass of confined gas are inversely
proportional, if the temperature remains unchanged within a closed system. Thus, it
states that the product of pressure and volume is a constant for a given mass of
confined gas as long as the temperature is constant. The law was named after chemist
and physicist Robert Boyle, who published the original law in 1662."

http://en.wikipedia.org/wiki/Boyle%27s_law

It is not just a good idea it is the LAW!!  (Of Physics :))

Of course there is some optimum size for the holes.

The whole idea here is the keep the frontal area down to minimize the aerodynamic
drag and use the slip stream to help cool the pipe. The configuration is somewhat
like a jet engine in that you are heating the gas in the outer pipe so in theory a
bit of thrust is created off setting the drag. One pound of thrust at 300 feet per
second (200 MPH) is 300 foot pound per second or 300/550 or .545 HP.

Paul Lamar

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