Archie wrote:
I broke down and sold my old dyno in favor of
new technology. No more sling psychrometer to
measure humidity, etc.
Fully computerized.
I need a bit of help.....
In setting up to play with rotaries, I need some advice
from those experienced in it, so that I am not reinventing
the wheel. Any tips, tricks, aids, or suggestions germane
to this particular engine would be appreciated.
Archie
Get in touch with Paul Yaw.
Paul Yaw <yawpower@theriver.com>
Paul Lamar
Paul Yaw wrote:
Hey Archie,
I'm not sure what help to offer. It should be pretty straightforward. I
can tell you what I use if that helps. We use a coupler that came from some
sprint car shop which slides over the splines on the GoPower brake. Another
splined shaft fits into that, and a clutch center section (spring hub.)
which is mounted to an aluminum disc. That disc bolts to a Midway
industries flywheel which then bolts to a stock Mazda automatic transmission
counterbalance.
I assume that anything you build will use this counterbalance rather than
the stock flywheel with a built in counterbalance, but if not you can get
into a bit of trouble here. If for instance you balance the motor with a
stock flywheel, and then later try to spin the flywheel alone to match the
counterbalance for use on the dyno, it will try to hop out of the
stanchions. You must balance the counterbalance with the shaft and bob
weights when you do the whole assembly. The Hines balancer spins at 500
rpm. If yours spins slower you will probably be OK. It doesn't start to
hop until about 470 rpm.
Also when you balance these things, you must find the center of mass of the
rotor with it full of oil. Since you can't get the oil to stay in place,
you can fill it with parrafin and then static balance it with a pair of
strain guage scales. You will find that it varies from about .080" to .120"
towards the gear side. We have to use two bob weights to get the required
mass, and there is no room to clamp them off center on the journal. Just
offset the beads in the bob weights to get the required distance off center.
The data acquisition is a DePac unit. The airflow meter which came with the
DePac is not very accurate below about 250 CFM, and so we use a large
venturi to supply the signal to the unit. Just about anything can be
adapted to the DePac if you calibrate it on the flowbench, and then adjust
the K factor in the setup file. Just make sure that its output very closely
follows a square function since that is how the DePac will compute it. If
you adapt another airflow meter, make sure that you test it at or near 60F.
The red and blue fluid in the Superflow flowbench manometers has its
specific gravity stated at 60F, and as you know, it varies a great deal with
temperature. If you bought a Superflow dyno, their airflow turbines (Which
seem to be VERY optimistic.) come in several different sizes. Roughly, a
rotary will require about 1.5 cfm per horsepower. Pretty ugly huh!
Make sure that your fuel flow meter is accurate at low flow levels as well.
Most of the problems I had getting setup had to do with getting accurate
results at these low air and fuel flow levels since most dynos are setup for
big motors.
The only thing I have found to be unique to the rotary is that it requires a
good heat soak before each pass to get repeatability. I think this has to
do with those big old cast iron rotors. Get the oil up to 180F, and Pull
it at about 75 lbs./ft. for 30 seconds or so before you let it rip. I also
make the pass at about 100 to 50 rpm/sec. Going faster than that seems to
hurt repeatability.
Make sure that you reset the inertia factor as well. These things are big
gyroscopes.
If the motor is flat, smooth, and toleranced correctly, the break in
period is practically non existant. If you have new bearings, or the
rotor/stationary gears have not seen each other before I would suggest a
typical break in period easing up to full power and rpm. In this case, I
normally drain the oil, and cut the filter open for inspection after break
in. It is very hard to keep the bearings round when you press them in. If
you find any copper in the filter, tear the engine down and check the
bearings.
Many V8 engine builders use dyno headers when testing an engine. I think
that is crazy with a V8, and just plain worthless with a rotary. Use the
exhaust system that will be on the motor when it is installed. If you build
a bridge port, or peripheral motor this is ultra critical.
Jim Mederer uses a Stuska/DePac setup, and in my conversations with him in
the past he has been very helpful and free with information.
Hopefully you got a DePac, and we can compare notes. If you bought a
Superflow, expect some big power and airflow numbers. I talked to one of
the Superflow guys at a trade show, and he actually admitted that the
results from their setup are "optimistic." I guess that's a nice way to put
it.
I would like to hear about your new setup. Please contact me at
yawpower@theriver.com
Paul Yaw
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