How would that differ from a throttle body downstream of the
compressor?
I think that must be what he has now. Perhaps he is opening the
throttle
wide now on takeoff and that is when he gets too much boost. Perhaps
someone
should tell him not to open the throttle all the way :)

Paul Lamar

The difference is that it is easier on the turbo, you don't have the
pressure backing up on the compressor.  I believe that this would be
the only throttle body you would need.

Hans

Not sure about this Hans,
The airflow through the compressor/engine and thus the boost would be
the
same either way. With a TB after the compressor you have a BOV to
relieve
the pressure when changing from full throttle to idle. If the TB is
before
the compressor, the stress on it would be roughly the same but you
would
need a vacuum release valve instead between the TB and compressor.
Since the
engine wants to create vacuum when slowing, you might have a
slow/delayed
throttle response this way.

Ron Freier

You may be right, but I don't believe that either is a problem.  Poorer
throttle response is definitely the case, but not a problem in a plane
where most of the operating regimen will be over 5000 RPM any way.  I
do think a vacuum is easier on the compressor than pressure, fewer air
molecules.  I don't think any of the turbo planes flying run a blow-off
valve.  It really is more of a device for abrupt decreases in the
throttle setting which is more of a need for auto applications.  Having
a throttle body upstream of the compressor is really not much different
than the old "wet" car systems with a carb upstream of the compressor.
IIRC (If I recall correctly) Greg Richter runs a pop-off valve set to
10 lbs between the throttle body and the compressor (conventional set
up with the TB downstream), and no wastegate.

For those that don't know, both a blow-off valve and a pop-off are
devices to relieve pressure  on the intake side.  A blow-off valve is
vacuum sensitive, so when you lift off say to shift gears, the vacuum
downstream of the throttle activates the valve releasing the pressure
between the throttle and the compressor, reducing stress on the
compressor blades, and keeping the pressure from backing up and slowing
down the turbo.

A pop-off valve is simpler, it merely opens above a preset pressure
limit.

Hans Conser

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