Ernesto related:
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
Dearest Chrissi,
I agree with you about the wastegate. I plan to use Greg's idea and put
an adjustable blow off valve on the intake manifold side and block off my
HKS wastegate port. A larger exhaust A/R will allow my boost to come in at
higher rpm's with the blow off valve only opening at the top end. A smaller
A/R will cause the boost to come in at low rpm and open the blow off valve
sooner........I think. How about the GT35 with a larger exhaust A/R??
Where's the turbo experts when you need them? :)
Ernesto
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