We tried using thicker pipe wall (600 series stainless
               in incremental
               increases in thickness up to almost 1/8" wall ) and even
               those would
               eventually crack.  The problem was not cracking at the
               flange, but rather
               cracking of the pipe wall itself itself whenever pipes
               from each port were
               merged outboard of the exhaust ports without any
               provision for a slip
               joint
               or other.  Before we came up with the idea of the ball
               joint welded
               directly
               to the port, we first used short stub stacks welded to
               the four stud
               flange,
               with a slip fit pipe over that and it completely
               eliminated the cracking
               problems even using .035  wall...but we never came up
               with anything close
               to
               elegant in terms of securing the stub pipe to the slip
               tube.  To test the
               approach we retained the exhaust tube to the stub stack
               using safety wire
               looped through small 'L" brackets welded to the outboard
               tube with a hole
               drilled in the 90degree leg for the safety wire...and
               the other inboard
               "L"
               brackets  held on the stub end by each of the four nuts
               that secured the
               exhaust flange/stub stack to the rotor housing.  Looked
               cheesy and not
               meant
               for long term but the approach did work and led us to
               the ball joint. It
               is simple and cheap if you could come up with an
               effective, safe way to
               retain the tubes.

               Steve Beckham


           Steve,
           Thanks for the response, I agree the pressed exhaust flanges
           are the most
           elegant option, but there are a degree of complexity for the
           average
           builder - whereas just welding may be easier. See attachment
           for what may be
           options. This isn't as you described (but similar) with a
           heavier tube as
           the stub I believe it would be quite robust- drawing by Bill
           Jepson.
           George (down under)



       George, I apologize for not being able to tell from this nice
       drawing by
       Bill....is the downstream tube allowed to expand and contract
       independent of
       the short stub stack?

       Steve Beckham


    YES Steve,
   The short header tube has the collar (with dog leg or L shape)
   welded to it.
   The exhaust pipe has a collar and small extension welded to it.

   The exhaust pipe is also flared to accommodate the short header tube.
   The L shaped ( dog leg) holds the two together. There would be movement
   between the two pipes which would allow for differential expansion and
   contraction, which I believe is your primary concern.

   This could design could have many variations, like more than one dog
   leg and
   springs, but I've never liked springs around that sort of heat.
   I believe it's a simple yet quite effective design that can be
   handled by
   the novice.

   Here is another by Bill Jepson, if you were concerned about gas leakage.
   Could be considered simpler.
   George (down under)


Paul,
Why not just drill the holes in the bracket a size or two larger than
the bolt to allow for expansion, but still be secured?   Dave D



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