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I have=20 a pop off valve on my installation which is there in the likely event = that the=20 waste gate can't dump enough boost. I agree with Rusty that a POV = is not=20 an acceptable method of boost control, but is a very good safety = device. I=20 don't really think that it would unload the turbine when it opens, = because of=20 two factors. One, mine pop off valve doesn't just jump open, it = starts=20 opening at 8 lbs, but takes about 10-11 before opening all the = way. Two -=20 even when open all the way, it is restricted by the outlet on just how = much it=20 can dump. It certainly wouldn't unload the turbine=20 IMHO.

If you=20 weight the option of having the POV valve open in flight vs over = boosting the=20 engine, it is a no brainer. I'll take the=20 POV.

Steve=20 Brooks

Hey=20 Rusty,

Do you still have that blow off=20 valve?

John

Never had one :-) =20

Technically, what I had was a "Pop off valve", or = "relief=20 valve". A = relief valve, is=20 just a spring loaded valve, that dumps pressure over a certain = amount. =20 This is used as a final safety valve on some cars, but not = RX-7's. A=20 blow off valve is something that's standard issue on turbocharged = cars, but=20 probably not needed on airplanes. A BOV is vacuum actuated, and is used to dump = the pressure=20 when slamming the throttle shut, such as between gear shifts. = This saves=20 the turbo from sudden over-pressure. =20

I=20 still have the relief valve, and I will certainly sell it to you, but = I have=20 to stress that this is NOT a fix to the problem. Opening the = outlet side=20 of the turbo causes overspeed of the turbine, which is bad, and this = is never=20 considered an acceptable method of turbo control. It also isn't=20 desirable for aircraft, because this is a differential device, meaning = that it=20 looks at pressure compared to ambient. In other words, it adds a = certain=20 amount of boost, which falls as you climb, just like a NA = engine. =20

I=20 would urge you, and everyone else that's trying to use a stock turbo, = to look=20 into modifications that reduce the boost level at low rpm. Ed = has posted=20 links to a place in Oz that does this, and I'm sure there are folks in = the US=20 that can do the same thing. Unless you can modify the turbo = to be=20 controllable, it's not safe. We don't want the Subaru guys = posting=20 your off-airport landing :-)

Cheers,
Rusty (I need a=20 plenum)

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