Old message 13 Jan 2000
Don Moncrieff wrote:
Thanks Chris for your 18 Dec. letter. I seem to be in a very similar
place with my 13B and am wondering very similar things about my turbo.
I'll be very interested in the conclusions and solutions you reach.
I'm trying to figure out the best thing to do with both the switching
valve and waste gate. Have you come to any conclusions yet?
You may have noted that Paul Yaw (thanks Paul) told me that I will not
be able to limit the boost because the wastegate and turbine are very
small.
So, if the wastegate is not needed and the switching valve is to help
reduce HC emmissions--what do we need? I suspect I'm displaying a lot of
ignorance.
You could control the boost with an add on wastegate, but I feel that
the stock turbo is VERY inappropriate for your application. The danger
is in overboosting the engine, and overspinning the turbo. Either one
is a bad thing. EVERY stock turbo that I have disassembled has had many
cracks in the turbine housing, and the manifolds usually crack sooner or
later. The aftermarket pieces like a TO4 are less prone to cracking and
are much easier to control because of the larger turbine. The bearing
section is also much more durable. The compressor wheel is bigger which
means lower rpm for a given amount of airflow/boost. You will need a
relatively large turbo if you wish to normalize your manifold pressure.
I don't know at what elevation the stock turbo would overspeed, but it
would be quite low.
If you turbocharge your AC engine, the turbo itself will be the most
highly stressed piece in the system. I don't think anyone knows yet
what the life expectancy is for a turbo on an AC rotary. My opinion is
that using the stock turbo would be dangerous. A TO4E 50 trim
compressor, P trim turbine, 1.0 A/R tangential turbine housing. will
work quite well if you use an aftermarket turbo manifold like the piece
made by HKS. If you build headers you will have problems controlling
the boost, and you will have to step up to a Q trim turbine, and may still
have to modify it to get everything under control. If you use the turbo
to normalize at high elevation, a turbo tachometer is mandatory. If you
spin them too fast ugly things happen. After all this, you may still
need to make a housing swap to get exactly what you want.
While I am on the subject, Bob Keller sold Turbonetics, and Rick Head
has left and formed his own company with Jon Myers and one other guy
from Turbonetics. My dealings have always been with Rick, and so I will
be buying from him in the future. An added benefit is the expertise of
Jon Myers who has been working with turbos since he was at Rajay years
ago. They are good guys, and they know what they are doing. The
company name is ITS, and I will post the phone number tomorrow. (I don't
have it here with me.)
Paul Yaw
Thanks Paul. I was wondering what was going on at Turbonetics as I had
some trouble getting some help there. I was considering Fastrax in
Torrance or Gardena as a source and dropped in yesterday to talk
to them. The main guy was in Japan so no luck so far. Fastrax has been
supplying the Garrett turbo's for Able Ibbara's 800HP 13B.
BTW aircraft turbo's housings are supposed to contain a burst turbine. As such they
are heavier. If your non AC turbine is oriented such that high energy turbine
particles exiting the housing could penetrate the firewall or a critical
part of the engine a SS & Kevelar shield would be a safety feature. You
will probably have to deal with an under the cowl in-flight fire as well.
Keep the turbo out near the side of the cowl with a SS fire shield
between it and the rest of the engine and firewall. The Kevelar
should be on the back side of the SS. Hopefully the SS will be merely
dented and not penetrated. WW II turbo's could explode
and the particles would not penetrate anything as the turbo's were mounted
near the outside of the cowlings with the turbine plane of rotation
tangential to the cowling surface.
Turbo RPM could be another input to the computer that controls
boost by means of a electronic waste gate. This literally would
be an ounce of prevention.
Paul Lamar
An update. The stock turbo's that don't crack are the 89-91. Paul
Yaw was referring to the 87-88 and the dual 1993 and later turbo's.
I am going to try the stock single 89-91 turbo first before I go to all
the trouble and expense of a TO4 and a new exhaust manifold.
Fastrax does not want to deal with you if you are airplane.
Paul Lamar
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