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

Dear Ernesto,
One reason I selected the GT35 over the GT37 was because the 35 had a matching flange to the TO4.
I will have to check on the availability of the 37 with the TO4 housing.
Realise too that Paul Yaw's choice is based on using a wastegate where you are dumping a lot at
sea level and it tapers off to some altitude. Then the boost tapers off above that. Without the
wastegate you balance the turbo to be optimal at some altitude. It's more conservative.
Since I really know nothing about the subject I am not locked in to any one choice but I have to
lean towards the one turbo 13B I know is flying and could ask some questions of. I don't mind
going to a bigger turbo and some form of adjustable waste gate. I do mind going to a bigger turbo
, adding an expensive wastegate and dumping pressure 90% of the time... means someone used
dynomite to do the job of a capgun and is opening all the doors and windows to reduce the damage.
One day you get distracted and don't open the doors and windows.
...Chrissi

Cozy Mk-IV 13B Turbo
www.CozyGirrrl.com
Chrissi@BlueMountainAvionics.com

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