On Wed, 15 Dec 2004 12:55:31 -0500, Boris Mohar
wrote:

||On 15 Dec 2004 00:22:22 -0800, "GriffithBuilt"
||wrote:
||
||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
||
|| I had a similar situation with internal wastegate hole it TD05 Cast iron
||turbo housing. I took it to a machine shop and they tried to drill out. It
||did not work. The drill just spun there barely making a scratch. It appears
||that part of the housing got altered over the years by constituents of
||gasses passing through it. I ported other parts of this turbo housing using
||a die grinder and had no problem. Finally I put a ball shaped grinding stone
||in my drill press and loaded the feed handle with an elastic band. It took
||some time but three stones later I had a 1" hole. I would appreciate if
||someone could explain the process that hardened the wastegate passage.

Turbo manifolds are often made of cast steel. They get a lot hotter and carry
more weight out at the end than regular manifolds.
Texas Parts Guy