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
Here is an excerpt from the latest issue of RX Tuner mag. Although we don't need
700 HP there are some "secrets" about the fuel system that I think we should pay attention
to. I had not thought of it before but if your wing tank fuel pickup becomes temporally
uncovered for whatever reason you could blow your turbo engine.
Seems the best thing to do is add a sump tank somewhere.
Paul Lamar
The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/
Copyright 1998-2004 All world wide rights reserved.
But, like every exceedingly tuned car, the project didn't just come together
overnight. For Ralph, the center of his tuning efforts was dictated . by the
choice of turbo. "I've tried four different turbos to get the power to the
level I wanted." And of course a change ,of turbo isn't a simple plug and
play operation. Each turbo will have it's own unique flow characteristics,
which mean unique tuning requirements. "It took around six months to get the
car rolling, and about a year to work out the bugs." Which actually is a
testament to the capability of the team at Groundzero. Very few tuners in
the world can lay claim to developing over 700hp on a 13B-REW block, and
this project was done almost completely in-house. Hold on there! "700hp?"
you say? Actually it's more like 800hp. Ralph's RX-7 has produced a maximum
of 712 rwhp @ 32psi on a Tn Q-trim, 1.15 AIR divided turbo built by XS
Engineering.
And that number was produced without the help of nitrous. When I asked Ralph
"Have you ever even used the nitrous?" His reply gave even more appreciation
for his tuning skills, "No, it's crazy enough as it is, it's stupid. I think
it's time to take the nitrous out. I run 25psi on the street minimum, I have
a 22psi spring in my wastegate. I was going to use it to spool the turbo,
well, turbos are getting so good that we don't need it. Now with this GT
wheel that'll spool even faster and flow more, I think it's time to get rid
of it and redo the interior." I keyed on the words GT wheel, "so you're
getting a new turbo?" I asked. "Yea, I think it's called a PT70GTS, 70mm GT
wheel, so it's a lot more aerodynamic and efficient than the Tn, and will
flow 10%-15% more.
The car should be pretty much dialed as it is, so it'll be running by
Monday." I'm writing this on Friday. In talking with Ralph, I almost feel a
bit stunned at how easy he makes it all sound. But I know it's anything but
easy to squeeze these kinds of astronomical number from a 13B, so there must
be some secrets. As we know, in a rotary, fueling and tuning is everything,
and Ralph has paid special attention to the fuel system. "We sumped the
stock tank, and run that into a pressurized surge tank. This keeps me from
popping a motor by running the tank to low and getting fuel starvation. All
it takes is a second and your motor is gone, the surge tank keeps the fuel
flow consistent."
Well, there's one secret. "Other than that, we run the Magnaflow 600 pump,
it'll flow some ungodly amount. We run a -12 and split into pair of -8s that
run into both rails, and then a -8 return. Running into both ends of the
rails keeps the pressure constant."
There's another secret, or more accurately, just tedious attention to
detail. And even with all this fuel system overkill, Ralph says his main
problem with each new turbo is getting the fuel system to keep up. "Right
now we're adding two new injectors. With our 850cc x two primaries, and
1600cc x two secondaries at 68psi base pressure, we were running 100% duty
cycle at 32psi of boost. So we're producing a totally new intake manifold
that will allow us to plumb in a couple more secondaries. For the GT turbo,
I'll probably run four 1,600cc secondaries, and drop the rail pressure back
down to 45psi or so."
Of course there's more to making 700hp than just fuel system and turbo, you
still have to tune, and you spark still plays an important role. Ralph uses
the tried and true combination of a Power FC and the Datalogit. To get the
low impedance 1,600cc injectors to work, Ralph put his electronics degree to
good use. "I just put some big heatsinks on the output transistors to keep
them cool, and that did the trick."
All the tuning is done by Ralph either on his in-house Mustang chassis dyno,
or on the street. Mixture is monitored by a FJO wide band. Ralph says that
he's done a lot of research into proper tuning, "I've run EGT's on both
front and rear rotor, and the rear seems to run 250 degrees hotter because
of the manifold layout and more air into the rear." So with his newest turbo
setup Ralph has developed a manifold that he says will equalize flow from
the front and rear rotors, and hopefully keep the mixtures even. "Every
motor I've blown has been the rear rotor, so we made this manifold to keep
that from happening."
More examples of iniquity can be found in the ignition system. Ralph found
that the car was easier to tune with no wasted spark, and by having no split
timing. "I tie the trailings together, and run no split. I ran the car on
the street this way for a year and a half at 25psi, and it just seemed
easier to tune." Other pieces used are a pair of MSD HVC ignition boxes,
combination of MSD coils and stock coils, and a B&M NuVolt to raise the
voltage to 22v.
