Generally speaking the 89-91 stock Mazda turbo setup is way
less prone to crack than any Mazda turbo and manifold before or since.

I did not notice it a year ago when I bought a 89-91 turbo
manifold in Sydney but it had a fine hairline crack on the
sharp edges indicated by the red arrows. When I was in Sydney
last week I picked up another one as they are only $50 US.
I inspected this one much more closely and I think it is free
of cracks.

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
 
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