> > > >  What wall thickness was the 321 stainless exhaust tubing  Keith?

 > > >
 > > > > Paul Lamar
 > > >
 > > > Keith Holm wrote:

 > > > > 16 gauge, or .065".
 > > > > Keith Holm
 > > > > Powersport Aviation

 > > > Wow! .065 thick 321 and it still broke in only four hours. Hard to
 believe.
 > > > Must have been a defective weld or he cantilevered the entire ridged
 > > exhaust
 > > > system off the flange with no braces and it vibrated at a sympathetic
 > > > resonant frequency. Either that or that PowerSport PP 13B is one
 powerful
 > > > motor :)
 > > >
 > > > Tracy got 650 hours out of this .035 thick SS muffler.
 > > >
 > > >  Paul,

 > > > There were likely many factors contributing to the exhaust failure.
 As I
 > > > wrote, the system was unsupported, and likely was in resonance.  There
 was
 > > > also no room to allow for the differential expansion of each header
 tube.
 > > > The weld did not appear to be defective, but there are problems
 associated
 > > > with welding thin wall tube directly to a heavier flange.  Pictures of
 this
 > > > will be up soon.  The system probably had closer to 20 hours on it
 > > > considering the extensive ground testing that Kerry performed.  You
 are
 > > > right of course that the Powersport RE-215 is one powerful engine, but
 not
 > > > in any destructive way!!
 > > > Keith Holm
 > > > Powersport Aviation
 > > >
 > > > Paul Lamar

 > Keith,
 >
 >   Are you saying that the failure was at the point where the head pipes
 > were welded to the exhaust flanges (at the engine)? If this was reported
 > before sorry for the repetition - I must have missed it. I'm putting
 > together a header right now using .065" 321 and had planned on slip
 > couplings where the primaries enter the collector. Sounds like maybe slips
 > should be considered at the engine end of the primaries as well.
 >
 >   Thanks very much for the info on this failure Keith.
 >
 > Mike Wills

 Hello Mike,
 No you did not miss it!  I apologize that we do not have more time to
 address questions on this list, but current business comes first!  I will
 answer your question, and have attached 2 pictures that show the failure
 clearly, the remaining pictures and report will be on our website soon.
  I suggest picking up a good book on welding, but in short, you should not
 weld the tube to the flange on the outside in a continuous bead.  The tube
 should pass through the flange and have a few tacks on the outside.  The
 tube should then be welded around its circumference on the back side of the
 flange. ( a chamfer here helps)  The flange is then made flat again on a
 belt sander.  Powersport takes things a step further by machining/turning
 our flanges from 321 to create an integral flange/tube component.  The first

 > 1" of our "tubing" is a machined part of the flange with a thin wall
 > section.  This thin walled "machined tube" can be welded with
minimal stress
 > to the 16ga exhaust tubing.

 Our EGT's are 1,650 @ max power, and close to 1,700 @cruise.  The location
 of your probe will give some variation to the readings. Ours are currently
 about 12" back.
 I hope this helps Mike,

 Keith Holm
 Powersport Aviation

Keith, sounds like you are running your engine too rich at cruise.
Tracy found he can lean to about 100 degrees lean of peak and the EGT
will drop down to 1450 degrees F or so. You should also benefit greatly
in terms of fuel flow and MPG. Not to mention lower stress on the
exhaust system. 321 SS is in a steep strength slide at 1700 degrees F.
Tracy feels the reason for the rotaries  ability to run lean is a
outgrowth of the rotating combustion that provides a radial stratified
charge.

Paul Lamar

Mazda Tricks advised me to insert the exhaust pipe completely through
the stock  flange and weld from  the backside.  I think they also
said to weld around the outside perimeter but I don't recall it
clearly.  When I changed my exhaust config, I cut the original
exhaust pipes an inch from the flange and slipped the new exhaust
pipe over it and welded  in all around. The old stub should act like
an internal heat shield.   However, one can never assume that it will
not break suddenly in flight  It is imperative that the entire
exhaust system stay in place, if that happens.
--
Jerry Hey

 
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