Chrissi said:
We have narrowed the turbo selection down to the Garrett
GT35 84
trim 0.94
A/R and GT37 82mm, 52 trim, 0.54 A/R or GT37-TO4 housing
76mm, 52
trim, 0.70
A/R as being the closest to the TO4e-50-P trim.
The drawing of the GT35 is it is a bolt-on with a TO4
manifold
footprint.
The GT37 with TO4 housing is ambiguous as to whether the
housing is
the
turbine or compressor section therefore the footprint is in
question.
I think the GT37 units are much closer to getting centered
on the
turbine
maps based on what we are guessing so far about performance
(Cliff
Manzke's
numbers)
The GT series is Garretts answer to the new performance
market. They
are all
ball bearing. Not sure if all turbine wheels in series are
inconel
or if that
is option.
My thoughts are this, although Greg's "no wastegate"
approach worked
for him,
if instead you go the wastegate route and use an adjustable
boost
controller,
although more expensive and complex to install, it adds an
extra
margine of
safety to the system and at critical times may be one less
thing to
monitor
and control. Going without means settling for "best guess"
and I'm
just not
one who is comfortable with that ambiguity.
Any thoughts, ideas, criticisms or advice?
...Chrissi
-Rotary RX-6 wrote:
Chrissi, I thought that you were after an A/R ratio in excess of
1.0.
Isn't the A/R
ratio in most sports cars far less then 1.0 for acceleration
purposes?
Aviation
turbos I believe are around 1.3. Please correct me if im wrong.
but the
smaller the
ratio, the faster it will accelerate to increase velocity not
volume.
????
This is such a great forum.
Disclaimer: I'm not an expert.
Funny this subject would come up today. I just finished reading
this web
page:
http://www.scuderiaciriani.com/rx7/turbos.html
A quote off this page:
"BTW, I wouldn't recommend anything smaller than .96 exhaust A/R
ratio."
When you read this page please remember that these guys are looking
for big
HP gains but some of the info applies. It is easy to get the HP we
want
(about 250 hp at about 405 CFM [or 32 Lb/Min] at 6500rpm, about 7 to
8 psi
boost from Paul Yaw's numbers:
http://personal.riverusers.com/~yawpower/ac13bt.html ). The hard
parts are:
1. Keeping the compressed air cool.
2. Not overspeeding the turbo.
3. And as we climb, keeping the compressed air cool and not
overspeeding the
turbo.
Solutions:
1. By looking at the chosen turbo's map, and staying within the
map's most
efficient range (high percentages) to keep the boost as cool as
possible
then using a big intercooler to cool it further. Also, bu using the
least
amount of boost needed to the do the job.
2. Airplanes use big exhaust A/R's. I would start with a big A/R 1.3
(looser) and then go smaller (if need be) to bring the Max hp level
down to
the Max rpm. Too small an A/R and you can overspeed the turbo.
3. By using your max CFM (about 32 LB/min) draw a vertical line up
on your
map for your chosen turbo. This will give you and idea of how high
you can
go without overspeeding your turbo by looking at the numbers
(pressure
ratio) on the left side of the turbo map. The highest point of the
line
within the mapped area's will give you the max pressure ratio (this
is the
max boost to keep sea level hp) before you overspeed the turbo or
where you
have to back off the boost, hp, or rpm to stay within the map.
Clear as mud ? : ). We can not go wrong copying Paul Yaw or we can
try
using the GT 35 (GT 37 will give more Alt and hp) with an exhaust
A/R of 1.3
(starting point) so we do not have to use a waste gate (we limit
boost with
rpm and blow off valve or bigger exhaust A/R). All turbine wheels
in GT
series are inconel. Both GT's cost about $1200. Expensive muffler,
huh!
Ernesto
Doug Mueller wrote:
I agree with you Ernesto, If you have never heard or seen racing up Pike
Peak with
autos, this is exactly the conditions that we expect to see under
standard
atmospheric conditions in our aircraft. I have been on top of Pikes peak
in the
middle of August and the temp up there is 37F or 3C. BTW Pikes peak is
14000+ MSL.
Doug Mueller
RV-6 13BT
N900DM
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