My recommendation is use a die grinder and radius this sharp edge.
I can understand why it cracks in this area as any sharp edges
are invitations for cracks to start. Especially when subjected
to high temperature gradients.

Paul Lamar

Paul,
Would you say this is potentially the case with a cast iron HKS manifold
also?
...Chrissi

Cozy Mk-IV 13B-turbo
 www.CozyGirrrl.com
Chrissi@BlueMountainAvionics.com

Actually I got the idea from looking at the HKS. I noticed large radii in all 
tube plate intersections. Now I have not seen the other side so I am
not sure they followed that design rule everywhere. If you get a chance please send
me a picture of the inlet side.

Perhaps HKS used sophisticated thermal finite element analysis which was perhaps
unavailable to Mazda back in the 80's and or Mazda compromised due to
manufacturing cost considerations.

The brute force or sledge hammer approach is to add another couple of pounds
and go up on wall and flange thickness everywhere. That certainly worked
for Ed Anderson's exhaust manifold made from .140 wall stainless steel pipe 
railing. That does not even discolor let alone crack or fail.
 
Paul Lamar
 
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