Ernesto Sanchez wrote:

All these choices with different options can drive a person crazy.

Thank

you Chrissi for sending the Garrett catalog.  I was thinking of

using TOE-50

or 60  Did you see the map for the GT7?  If you draw a vertical line

up from

32 Lbs/min it looks like it would be hard to over speed at altitude

and looks

like it would be more efficient (less heat).  The TO4 housing 76mm,

52 trim,

0.70 A/R has the best pattern. The turbine with 1.12 looks good too.

I

think the only way to be sure is to dyno them in an altitude

chamber.  I

wish I had the money.
Ernesto

Dear Ernesto,
Some notes from chats with Greg were that he was seeking a pressure

ratio less than 3.0 and an A/R

in the neighborhood of .81 to stay clear of the surge range and closer

to the middle of the map,

that a 1.0 A/R pushes too close to the edge of the map.
...Chrissi

Please take everything I say with a grain of salt.  I'm not an expert by any
means but here's Paul Yaw (who builds and dyno's 13b turbo motors)
describing an aircraft 13b turbo motor he built:

"The turbo (From Turbonetics) is a Garrett TO4E, 50 trim compressor, P trim
exhaust, with a modified 1.3 AR ratio housing. The turbine wheel is made of
inconel. The center section is water cooled. The turbo feeds the engine
through a small intercooler made by Spearco.
Boost is 6.4 psi at 6500 rpm. (43" Hg. manifold pressure.) Boost is
controlled by a Turbonetics "Deltagate"

End of quote.  Here is his web site:

http://personal.riverusers.com/~yawpower/ac13bt.html

Correct me if I'm wrong:  I get a corrected pressure ratio of 1.6 (left side
#'s of compressor map) for 8 psi of boost.  Air flow is about 32 lbs/min
(bottom #'s of compressor map).  As we climb the air gets thinner so to get
the same psi we have to make more boost (pressure ratio goes up).   The GT37
appears to be more efficient (less heat and less likely to knock or ping) as
you climb and less likely to over speed (explode).  

The exhaust A/R for the
GT37 is 1.12.  Paul yaw is using 1.3 and he is an expert.  I think the 13b
is different in that there is more un-burned fuel in the exhaust and it's
still burning (expanding) so you use a larger A/R.  Also, I was told on this
list that certified aircraft use A/R's larger than 1.  Again with a larger
A/R you are less likely to over speed at altitude.  I'm not sure but I think
I read an article in Contact where Greg said his intake manifold heat is
high and he is dumping alot of air.  His turbo may be on the small side but
again I'm not an expert.
Ernesto

 
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