Here are a couple of T3 maps. Ironically a bigger compressor might
help (I
think).
A turbo tachometer would help us match the turbo.
Paul Lamar
Bulent Aliev wrote:
Paul, I was thinking the same thing. Can we fit a bigger compressor on
our
turbos? I see on ebay T4 compressors for sale, but my practical turbo
knowledge is nill?
Bulent
Yes I think we can. As I recall from a message about a year ago there is
someone in Australia doing just that. I don't know if a T4 compressor
will fit on a stock 1991 turbo however. We could also just put a muffler
on the turbo to slow things down with back pressure.
According the Hugh MacInnes book Turbochargers as a rule of thumb a
turbocharger
picks up speed at the rate of 2% per 1000 feet. At 10,000 feet it is 20%
higher RPM.
Since centrifugal force is proportional to the square of RPM the stress on
the blades is 44% higher at 10,000 feet all other things being equal.
At 15,000 feet it is 225% higher. This is mitigated somewhat by the colder
temperature at higher altitude but your turbo is more likely to explode
in the warmer climates :) We must design for this.
To follow along on this you will need Hugh MacInnes book "Turbochargers".
Page 37 Sea level.
150 cu in/ 1728 = .0868 cu foot
0.0858 X 7000/2 = 303 cubic feet per minute.
Hugh is assuming 100% volumetric eff. here. We may be higher.
He assumes most engines are 80% VE so he adjust for that. We won't and
will stick with 100% in this case.
For 10 psi boost and 65% compressor efficiency.
(10 X 2.03 +29)/29 = 1.7 pressure ratio.
from table 1 page 16 Y = 0.162
0.162 X (70F + 460F) = temp rise in degrees Rankin or 202F
Density ratio is 1.36 actual compressor inlet flow is therefore
1.36 times 303 or 412 cubic feet per minute.
Converted to pounds per minute that equals 28.42
You plot this number along with the pressure ratio on a
turbo map. This looks like it won't fit well on any of the
T3 maps. This is probably our problem. In fact this point
falls off to the right of almost all the T3 maps. We could
easily be getting 150,000 RPM at altitude.
Given this the right map is T04E "54" trim at 80,000 RPM.
Max RPM on this turbo is 115,000 RPM. Perhaps a TO4 "50"
trim might be safer also at 80,000 with max RPM 126,000.
Dave, what trim is that TO4 turbo you have?
This needs to be redone for altitude. In fact we need to do a spread
sheet or a QB program to calculate this for all altitudes and inlet
temperatures. Anybody want to take on this job?
I think Dave's inlet temperature is around 140 F as I recall.
Paul Lamar
A blast from the past:
Ernesto
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 the 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 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 allot of air. His turbo may be on the small side but
again I'm not an expert.
Ernesto
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