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Message
Hey Rusty,
Do you still have that blow off
valve?
John
Never had one :-)
Technically, what I had was a "Pop off valve", or "relief
valve". A relief valve, is
just a spring loaded valve, that dumps pressure over a certain amount.
This is used as a final safety valve on some cars, but not RX-7's. A blow
off valve is something that's standard issue on turbocharged cars, but probably
not needed on airplanes. A
BOV is vacuum actuated, and is used to dump the pressure when slamming the
throttle shut, such as between gear shifts. This saves the turbo
from sudden over-pressure.
I
still have the relief valve, and I will certainly sell it to you, but I have to
stress that this is NOT a fix to the problem. Opening the outlet side of
the turbo causes overspeed of the turbine, which is bad, and this is never
considered an acceptable method of turbo control. It also isn't desirable
for aircraft, because this is a differential device, meaning that it looks at
pressure compared to ambient. In other words, it adds a certain amount of
boost, which falls as you climb, just like a NA engine.
I
would urge you, and everyone else that's trying to use a stock turbo, to look
into modifications that reduce the boost level at low rpm. Ed has posted
links to a place in Oz that does this, and I'm sure there are folks in the US
that can do the same thing. Unless you can modify the turbo to be
controllable, it's not safe. We don't want the Subaru guys posting
your off-airport landing :-)
Cheers,
Rusty (I need a
plenum)
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