George Lendich wrote:
Paul,
Just had some feed back on Turbo selection and was advised that the
TO4E-50 is a good selection for power, however the housings A R are
.6 for the compressor inlet and .96 for exhaust inlet ( less
than the 1.3 previously advised).
However that would run a fairly high boost and would be too high for
just normalising ( N.A rotors) unless a wastegate is used.
My contact uses Mazda components which has the cost advantage - he
uses a 13B compressor with a 12 A turbo which spins-up more quickly
and provides more power sooner.
I advised him of our problem and he suggests that what we need is the
opposite to what he uses and that is a 12 A compressor with a 13 B
Turbo.
Their interchangeable apparently!
These are only suggestions of someone to try and it's either this or
the more expensive aftermarket set-ups.
I'm not using a turbo but would personally try the 12A compressor
with the 13 B turbo myself if cost was a consideration.
Just some feed back to consider, hope it helps.
George (down under)
Reeves Callaway wrote:
I have seen no mention of this technique in the newsletter, so I
thought I would contribute some thoughts on turbocharger selection.
One of the damnable aspects of turbo sizing is trying to come up with
the best compromise for the dynamics of manifold pressure generation:
how much, how quickly, how efficiently, and how costly.
Automotive turbo applications are driven by a much different set of
goals, primarily their wide-range dynamic response issues. The
aircraft turbo application is a much happier equation to solve,
whether it be for all out power, or altitude compensation. In fact,
there is an opportunity to closely optimize the performance of all the
components so that some real magic begins to happen.
It's possible to size a turbocharger so that the engine, as a complete
system, operates in 'crossover', that is, when intake manifold
pressure exceeds the exhaust manifold back pressure driving the
turbine. The result is a net positive scavenge flow through the cycle
and the result is significant gains in power. Combined with the right
intake/ exhaust event timing, BSFC benefits as well. This crossover
condition can only be achieved in a narrow band of operation, but it
happens to be the same band that aircraft engines are looking for: Part
throttle, medium load, and medium rpm ( as a % of max rpm)
A program goes something like this:
Select the 'frame' size, or family of turbocharger so that there is a
good selection of turbine wheels, turbine houngs, trims and compressors
available in the range of mass flows necessary. The Garrett T04 is such
a family. Then, generally on the dyno, the turbine side of the
turbocharger is selected for its swallowing capacity, resulting in
larger than normal A/Rs. The objective is to use all the gas flow to
drive the turbine, not bypass continuously through a wategate. (The
wastegate and its sizing still must function as a safety/ control
device, and for temporary demands for higher manifold pressure)
The compressor selection can now be optimized for its output mass flow
and tailored for its best efficiency. The simplest way to verify the
component selection is to monitor the exhaust manifold pressure just
ahead of the turbine inlet, in fact the port can sometimes be
coincident with the EGT probe location. A small damping orifice,
around .020 seems to work well, will give steady readings at the gauge.
A similar set up on the intake side, both before and after the
intercooler. Then you can go to work mapping the relative pressure
results vs. a whole range of operating parameters, load, speed, temps
et al. When you hone in on crossover, even if its only a .5 psi
differential, watch what happens to all the other numbers. If you can
achieve a 2, 3 or 5 psi lower turbine inlet pressure relative to intake
manifold pressure, then you've really done a good job. You'll see it
in the power, the temps, the bsfc, the ignition timing.
The resulting turbo configuration will be a hybrid: an unusual
combination of turbine and compressor, most likely much bigger on both
sides that the automotive application. And operating in speed and
temperature ranges that are comfortable, safe and unstressed. My guess
is that none of the stock automotive turbo components will be there in
the end. The material specs are just not high enough ( anyone who flies
without an Inconel wheel is asking for it...) The power and efficiency
numbers will be dramatic, the turbo application is truly in its element
once this balance has been achieved, and the near steady state
operation of the IC engine is one of the few times we as engine
development engineers can come close to this near perfect condition.
Reeves Callaway
Thanks Reeves. I greatly appreciate your sharing your vast experience installing
and tuning turbo chargers.
Paul Lamar
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