MSD 7531 Programmable Digital-7 Plus Installation - Manual (Page 19)

INSTALLATION INSTRUCTIONS 19
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Average Column: This column puts a filter of sorts on the data. The setting is defaulted to one,
meaning that you are viewing the raw data the same as in the History Trace Window. Increasing this
number averages the samples together for a cleaner, easier to read trace. This is done by averaging
the trace data which is 720° (crankshaft) average data. The Slope function requires an average setting
of 5 or more while the RpmDiff trace is best if viewed with an average of 5-10. Note that too much
filtering will distort the data.
Color Key: To change the color of a trace, click the pointer just to the right of the value column for
each trace in the Trace or Analyze box. This will bring up the color chart.
TIPS ON HELPING PROGRAM A SLEW RATE REV LIMIT
When the Slew Rev Limit values are set properly, the only time the limit is activated would be when
the clutch or tires cause an unexpected rate of acceleration. The Slew Rev Limit will try to control
the acceleration during these abnormal moments. Following are tips on programming a Slew Rev
Limit.
Get a good baseline run with the Slew Rev Limiter turned Off. Make sure the tune up on the car,
clutch setup and gear ratio are all consistent.
Analyze the RPM Slope with the average number set to 2-4. Locate the largest RPM Slope value
for each gear.
Program the RPM Slew with the largest value measured for each gear.
Program the Low RPM Margin to 200 rpm and the High to 400 rpm for an engine that rev limits
around 8,000 rpm. For every 1,000 rpm above 8,000 increase the High Margin by 50 rpm.
The Hold Count value default is 10 which is good on engines that limit up to 8,000 rpm. For every
1,000 above 8,000 increase the Hold Count value 2-3 steps.
Make a pass with the Slew Rate Rev Limiter On. Save the acquisition file and analyze the RPM and
Rev Limiter data. Reviewing the RPM Slope, RPM Value and Rev Limit Sum are key traces when
setting the Slew Rev Limiter.
If the Slew Limiter is activated only near the maximum rpm, check the Max Rev Limit setting. If it
was not reached, the High Margin setting should be increased. If the Slew was activated within the
first 100-milliseconds of the run, use the Launch Inhibit time program to delay the Slew function.
If the rev limits are close together and the Slope stays below the programmed Slew value, the Hold
Count needs to be increased to correctly position the Slew RPM target.
If there are a number of rapid rpm rates above the programmed Slew value for more that one sample
(without limiting) the Slew limit may need to be set lower as well as the Hold Count and possibly
the Margin settings.