Finn,

I think the flange does make some difference, just don’t know how much.  The reason I think that is that the stock manifold has slotted holes at two of the exhaust ports, allowing for the engine and/or the manifold to move/grow without affecting the other or breaking the studs.  I did the same thing on my exhaust system. 

 

The bends came from R.G. Wagner and is 304-SS material, the same stuff that Ed Anderson has used successfully for many hundreds of hours.  They are about 1/8” thick which absorbs much of the heat stresses, similar to a cast iron manifold.  Each bend passes through a close tolerance chamfered hole and is welded on the back side nearest the exhaust port. I didn’t wrapped it so that I can inspect for cracks and to allow the heat to escape.  So far, no cracks.  I do have a Zetex aluminized fabric heat blanket on the upper and lower cowl in the vicinity of the exhaust.  It made a significant difference in cowl temps.   

 

Mark S.

 

 

Sure looks good! Too good to change.

I don't think that the flange has much significance.

Time will tell, but you may find that the thermal stresses are where the bends are welded to the collector.

Now, you do have fairly long bends which may absorb the expansion. Then again, the length of the bends may make it worse.

A lot of factors here: difference of EGT of the three rotors, airflow over the outside of the bends and collector, vibration, etc.

In any case, please keep looking for cracks in the collector where the bends are welded to it.
If so, you'll have to at lease cut two of the bends at a straight point (near port?) and slide pieces of tubing over the cuts. Better would be to add actual expansion joints.

How thick is the material of  the collector?

If this were a pusher, definitely safety wire the collector!

Finn

Mark R Steitle wrote:

Finn,

 

Maybe that’s why some of the aftermarket flanges are one piece.  That’s how I made mine for that very reason.  So far, so good.

 

Mark S.

 

 

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

 

 

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