Ground running won't necessarily get you into that thermo cycle range. Seems you consistently have to get above 5,000 RPM before anything happens.

No expansion joints: it will crack.
Unless you use ridiculously thick material. Which is probably why the stock Mazda manifold is so heavy.

Finn

Bob White wrote:

Hi Joe,

Great story.  Glad you were on top of everything and made the right
decisions.

I have a similar exhaust system I think.  Two short tubes into a large
can. On mine, the short tubes are 0.065 321 SS.  After 5 hours of ground
running there doesn't appear to be any deterioration, but it's
definitely something to keep an eye on.  Which was made more difficult
by the insulation I just added.  I think I will install one of my
'J'Thermocouples on the insulation just above the exhaust system.  That
temp should spike if there is any crack in the exhaust.  I also have
cool air flowing thru the center of the can but so far I haven't seen
much flow because of the low speed operations.  A lot of hot air flow
out after shutdown though.

Thanks for a great report.  Maybe we should plan a rotary fly-in at
Hyannis, Nebraska. :)  How many rooms did that hotel have?

Bob W.


On Tue, 25 Jul 2006 21:55:08 -0700
"Joe Hull" <joeh@pilgrimtech.com> wrote:

  

You definitely need expansion joints. Tubes sliding within tubes, or
some other type of flex joints.
The thermal expansion/contraction simply kills those short runners.

Finn
      

Yep, I'm re-doing the whole exhaust system. No more inconel and no more
tangential collector.  It's probably going to be 2" x .065 wall, 321
Stainless tubes going to a collector and muffler of some sort. I seriously
like the idea of non-welded joints - nothing to break off!

Joe Hull
Cozy Mk-IV N31CZ (65 hrs - Rotary 13B NA) 
Redmond (Seattle), Washington



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