I've done this a number of times on Buick GNs and a die grinder is the only
way to go... but...be careful to first mark the WG pucks contact area before
you begin to enlarge the hole.
More often than not, the puck does not close exactly centered over the
existing hole in the exh hsg. Usually you'll see a carbon track there on the
exh hsg to indicate where the puck hits it so grind an equal amount
concentric with that carbon track to be sure you don't get into an area that
the puck can't close off.
As for the carbon hardening the casting, though I'm a machinist and not a
metallurgist, I douldn't think that could be possible but repeated heat
cycles can work harden the casting which in this case is what I believe has
happened.
Thanks,
Steve Monroe

"Steve Lusardi" wrote in message
...
I wouldn't change it at all, unless you have to. I would install a boost
pressure gauge and maybe an EGT gauge as well. They are inexpensive and
chances of the stock turbo overpumping is slim to none, considering how
conservative the factories are.
Steve

"GriffithBuilt" wrote in message
ups.com...
I have an old exhaust manifold for turbocharging a vintage BMW and I'm
running into a trivial difficulty with the wastegate flange. It's a
two bolt flange with a 22mm hole in the middle for the wastegate valve
to seat against. It's a leeetle small and I'm worried about boost
creep (engine getting higher psi than intended due to bad flow out the
wastegate). So I need to modify the circular hole to be around 32-38mm
in diamter instead of 22. Options obviously are use a flycutter to
machine it out or simply use an air powered die grinder (low tq, less
chance of mangling it) to grind it out after stenciling a template over
the existing hole.

Thanks for your time,

Jason