Cutting that divider would cause cracks in your turbine housing
 Dave. Don't do it. That is the problem with the 86 to 89 manifold and
 turbo set up.

I was thinking more along the lines of an appx. 1" circular hole ground
through the divider early in the exhaust manifold, leaving the turbine
housing untouched.  This would allow some of the exhaust gasses to "cross
over" before entering the turbine and use the second waste gate.  One smooth
round hole in the manifold shouldn't seriously increase the risk of cracks in
the manifold, and I cant imagine a crack would extend into the turbine
housing.  This will somewhat defeat the purpose of separating the exhaust
(low rpm boost), but we don't need that anyway.

I just dont know enough about the math to know how big to make the hole or
how such a hole would affect the tuning of the exhaust.

Dave Leonard

I think it would Dave. I don't think that is a good idea. Obviously Mazda
worked hard on that new manifold design. The first go around was a disaster 
so if you mess with that manifold you are asking for trouble. I envy you  having 
that engine. I would hate to see that manifold crack. It must be a work of art 
as Jeff has overestimated its weight by three pounds :-)

I don't see any problem opening up the waste gate holes however. Also a little 
back pressure with a butterfly valve  on the exit pipe would simulate the stock 
mufflers and catalytic converters to limit the pressure across the turbine. 

Paul Lamar
 
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