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Measuring AFR while under WOT was a major concern.
Fortunately the DIY WB became available toward the end of '01.
I built a copy and installed it in Dec. It works as advertised
and has been running happily ever since. |
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The installed Radio Shack box looks like this: |
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The sensor itself is a Honda part: |
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Total project cost was around $300 complete
and running; including the WB Unit, sensor, O2 bung, welding,
logger, and tach box; excluding laptop. Sensor was installed
in the Y-pipe (below): |
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Once the AFR info was in hand it became obvious that
Diacom ALDL logs were not of sufficient accuracy (~7 data points/sec)
to permit detailed tuning & evaluation of results.
Next I built a Tach transducer, so I could log AFR
and RPM info together. Tach box uses a National Semiconductor
chip similar to the circuit below:
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The last piece needed was the Dataq A/D converter,
which takes voltage outputs from the WB & Tach units and
records them in realtime on a laptop. The combination allows
test runs to be made while driving. |
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The Dataq board is a complete 4-channel datalogger
(priced at ~ $30), and comes with its own software.
Here is an example of an acceleration test made from
a rolling start in second gear. All testing is done on the same
piece of road, so results between programming changes are easy
to compare. WB volts shows the AFR at each RPM band @ WOT. The
slope of the RPM curve gives the power output of the test. Absolute
power output can be estimated by calculating delta Kinetic Energy
(1/2 mV*V) for each RPM band.
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Recording data with the Dataq at 120 samples/second
gives enough accuracy to evaluate changes in fuel and timing
curves.
An excellent resource to learn more about dyno results
is in the Tuning and Tech Articles at PUMA Racing: http://www.pumaracing.co.uk/mainmenu.htm
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All testing is done on an empty section of private
road with proper concern for safety. |
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