Swirl Meter For Testing Cylinder Heads for Intake Air Motion
Theory:
For years engine builders have
seen heads which flow great on the bench get beat on the dyno and the track by
heads with less flow. Obviously there is more to cylinder heads than just great
flow numbers.
One important
aspect for great performing heads is the motion of the incoming fuel/air charge.
Generally heads with good motion or swirl will perform better because they will
burn the fuel/air mixture faster. The Swirl Meter lets you measure intake
mixture motion on your flow bench to track differences between just good heads
and
Great heads. No doubt you’ve heard about "fast burn" heads
or the advantage of dual plug heads which also burn faster. When heads burn
faster you gain in 2 ways:
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The engine will require less spark advance. By firing the mixture closer to
TDC there will be less cylinder pressure to fight the piston rising to
reaching TDC.
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The burn will be completed sooner after TDC. This creates more cylinder
pressure after TDC to push the piston down and make more power.
Both of
these effects result in a more efficient engine
making more power out of
the same amount of air and fuel.
In racing you want to maximize the efficiency of the engine
because the result is more power. This is especially important in restricted
classes of racing where restrictor plates severely limit air and fuel flow.
Description:
Our Swirl Meter
has steadily been refined. For 1999 we added a 3 position switch. In the top
position the display updates every half (0.5) second. In the middle position the
display averages and updates every 5 or 10 seconds (user selectable by internal
dip switch). Hold it in the bottom position and you are shown the Maximum,
Minimum and Average for the 5 or 10 second period. This is useful to see how
stable the swirl was.
Other features of Performance
Trends’ Swirl Meter include:
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Low "flow restriction"
design lets you measure swirl at the same time as intake flow (big
time savings).
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Shows direction of
swirl, either clockwise or counterclockwise (counterclockwise is
indicated as a negative "-" number).
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Rugged aluminum and stainless steel
design with 20,000 RPM rated bearings designed to hold up in a shop
environment.
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Repeatable, large, easy-to-read digital
readout from -9999 to 9999 RPM with 1 RPM resolution.
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Low friction bearings provide for more
repeatable readings.
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Tumble fixture
available for more
"in depth" measurements and analysis.
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The Swirl Meter
mounts between the bore adapter and the flow bench and records the gross axial,
circular motion of intake. The standard 3.75" paddle wheel is designed for bores
in the 4 to 4.5 inch range. Custom paddle wheel sizes and designs are available
from Performance Trends.
The Swirl Meter
does not restrict flow significantly (usually less than 1 CFM at 400 CFM flow).
Record the Swirl RPM as you run your flow test and record CFM on the intake
port. (There is no use recording swirl when flowing the exhaust port.)
Some users make 2 tests, the first without the Swirl Meter to more accurately
record CFM without the slight restriction, then another test with the Swirl
Meter to record Swirl RPM only. You may want to check the difference in CFM with
and without the meter on your heads and decide if 2 separate tests are
necessary.
It is important
to realize that swirl readings are still relatively new to race engine
development and there is no "magic" Swirl RPM to design for. Tests have
indicated that you can have too much swirl for some engines, and
some successful engine builders actually design for low swirl.
Do not
simply design for maximum swirl without regard to flow or how the engine behaves
on the dyno.
Swirl readings will change with test pressure and CFM flow, distance
meter is spaced from the head, clearance between paddle wheel and bore
adapter, weather, bearing friction and temperature, etc.) It s important to be repeatable in your testing procedure when checking
for minor changes in swirl. When comparing Swirl readings with other
engine builders, be sure to consider these differences also. Performance
Trends is developing corrections and recommendations as swirl readings
become more common.
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