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