In a message dated 2004-01-13 10:13:57 AM Pacific Standard Time,
troy.jenison@... writes:
>
>
> With a CV carb on the dyno, you're right the slide may not be all the way at
> the top for all rpms. But, the throttle is wide-open during the test, (i.e.
> the butterfly is completely open) if the person running the test is doing it
> right. At any rate, it should only be when you first whack the throttle at
> low rpms during the dyno run the slide won't be at max open.
>
>
Lets also remember that for most commercially available dynometers, if you
try to tune your carb based on dyno figures more often than not you will have a
bike that is jetted to rich for the street. Second, its rare that a carb setup
alone is going to produce enough of a change to push the readings outside the
dyno's margin for error and until you get the difference between two readings
outside of the margin for error you really have nothing that you can go by in
making real comparisons. And with most dynos where you rent time it will be
rare to find that the owner has spent the time and money to make sure the dyno
is calibrated for the daily changes in temperature, air pressure and humidity
- this is usually left for the customer to pay for if the customer wants exact
results. Failure to do the calibration increases the margin for error. All
you have to do is attend a couple of drag races to realize how the weather
effects engine performance and to get honest readings from a dyno it has to be
calibrated to compensate out these differences so you have true apples to apples
comparisons when looking at different data runs.
Operating in that imprecise environment the only way to determine if there is
any real difference between the setups is to make enough runs, without enough
different bikes so as to have sufficient data to make a statistical call
based on a quantifiable difference in means, averages, or variation between the
two sets of data.
The basis for such a test would start by stating the hypothesis that the
opened air box/modified carb/aftermarket exhaust will make no difference. If this
hypothesis is true then statistics tell us if we take an adequate number of
samples we will have a mean, average and variance that we can compare to prove
there was no difference. Then, using statistics for the stock bike, you
calculate a margin of error for comparing the mean, average, variance. If the results
of the before and after sets of data have a mean, average, variance that
falls within the margin for error you accept the hypothesis. If the after data has
a mean, average, variance outside this margin of error then you can conclude
that there was a difference. The lsat thing to consider, once the margin of
error hs been calculated, it is tweaked to provide your confidence rating in you
conclusion. Typically this means after calculating the margin for error you
increase it to the point that if the after results exceed this value then you
can by 95% confident that your statistical test has proven something that can
be applied to the real world.
And here is some additional food for thought. Horsepower is not measured, it
calculated. It is the mathematical product of the rpm and torque at that rpm.
You can understand just what that horsepower will feel like by taking a good
look at the torque curve. The steepest part of the torque curve is where the
meat of the engine lives - the steeper the curve the harder the hit. As the
torque curve flattens out the engine starts producing less horsepower for each
step increase in rpm - typically this would be a good shift point to get your
best acceleration.
Pat
G'ville, Nv
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