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 > I don't think you could have varible vanes associated with the hot
>side without mucking up your exhaust gas scavenging for the piston
>engine.  If you closed down the flow area you'd be choking off your
>exhaust.  There are turbine engines that have this feature(the AGT-1500
>>engine used in the M-1 Tank), but they don't have the added complication
>>of of having to satisfy the flow requirements of a piston engine while
>making the turbine run efficiently.  The materials required to allow
>smooth operation at the kind of temperatures encountered in the exhaust
>stream, are exotic cobalt alloys which are probably cost prohibitive for
>an automotive application.

This post is incorrect in assumption and reality.  I might suggest that those
interested in VNT get some reference material.  Speculation isn't necessary.
In fact, HOT SIDE VNT has been widely proven in automotive applications, and
is extensively used in truck apps.  ALL using the hot side to vary A/R ratio.
For all intents and purposes, VNT has been, and continue to be a HOT SIDE
device, NOT a cold side one.  IHI (mitsubishi) sold the most in the Dodge's of
the late 80's (in the lowly Shadow ES no less).  There is some 'increased
turbulence' (not do to choking, more to do with vane tolerances not closely
directing exhaust gas flow) but with that comes some really increased
efficiencies and torque output with little lag.  BTW, most Garrett turbos are
integral wastegate, which also creates turbulence.  

There are at least a half dozen ways VNT was designed and implemented over the
past 12years on the hot side of the turbo.  I am aware of only 1 cold side
implementation, and I don't believe that to be commercially available.  Why?
Cuz the cost is triple a conventional hot side VNT.  There is information
posted from me and others regarding turbo technology available in the

Must admit, this is one of the more bizarre threads on this subject I've seen
to date here.  Do yourself a favor, get Bell's book (or a plethora of others),
the 'speculation' indicates some basics to turbo theory need to be understood.
VNT is a really basic concept regarding A/R.  

My .02

Scott Justusson