the
choice of the ignition timing in the kart is very important both
in the phase of the engine development, both in the fine-tuning on the track, where it is often overlooked in favor of the single
carburetion. In general all spark-ignition engines,
they are 4 or 2 strokes, the ignition has always played a role
fundamental for getting the best performance from the engine.
But while in the 4 stroke engines the choice of the ignition timing is
made "only" to obtain the best conversion of the energy
developed by the combustion into mechanical work, and then in power
to the crankshaft, in the 2 stroke engine at this purpose is added that to
to obtain the right exhaust gas temperature to do work at
the best the expansion chamber and to obtain therefore the maximum trapping ratio of the engine.
This second goal in the 2-stroke engine becomes predominant
because if the exhaust is not working well and then the trapping ratio collapses, at that point
also a proper ignition timing to obtain the maximum work
mechanic, changing a little the performance, what explains because the
ignition with variable timing for two-strokes are designed
right to try to do work at the best the exhaust on a rpm range
broader precisely by altering the exhaust gas temperatures
thanks to the ignition timing.
Let's figure from a technical point of view the problems that
meet in the choices of the ignition timing of the kart and hence as
move to get the best result.
In kart are used two types of ignitions, at timing
fixed and at variable timing usually in the categories
single brand.
In both cases the approach is the same, since that the
ignitions at variable timing are not reprogrammable, so the
work that can be done is to shift as those to timing
fixed.
HOW TO CHOOSE THE IGNITION TIMING OF THE KART
Technically speaking when a kart engine is developed, the three
factors, carburetion, ignition timing and geometry of the exhaust system
should be designed to have the total tuning and then at the engine speed of
maximum power the carburetion should be targeted
to provide the best combustion efficiency, the ignition timing to transform at the maximum the energy developed by the
combustion, and with the temperatures of the exhaust gases that deriving therefrom, the
expansion chamber should work optimally to generate the
maximum trapping ratio.
Obtained this, the torque at low speed and the power in overspeeding of the karts come
consequently in funcition of the characteristics of the engine, and, in the case
of ignitions timing variable, depending on the choices of
the timing made for altering the temperature at the high speed of
operation.
Obviously moving the ignition timing of the kart, change
the evolution of the combustion and the temperature of the exhaust gas,
then at each engine speed there are new balance, and the dyno charts
inevitably change, so the first thing
to do is to check if the ignition timing that is initially set
for the engine is actually what creates the torque curve and
the better power for your needs.
When we talk about the best dyno chart, does not mean that
reaches the maximum power, but one that in the range of
operation, provides averagely the torque and the power best. If
you have a dynotest, fixing the jetting, you should make
a series of tests with different ignition timing, and
compare the dyno chart in the view of how
the engine will work on the track.
This work will allow two things, the first to choose the value
ignition timing of the kart that allows us to obtain the dyno chart
more suitable for your use, and the second to know how to play with
the timing for a specific track, compared to another (more
torque in low, more high speed, more power, etc.).
At this point has been done the first part of the work, that if you
have a dynotest, and you have the appropriate expertise in the
choices, is the easiest part. The hard part is then how
manage the ignition timing on the track, under varying
atmospheric conditions. In fact, usuallly the dynotest are made on
standard atmospheric conditions, but what happens to the combustion
of the kart when changing the pressure, the temperature and the humidity?
As you know the weather conditions require for first an
adjustment of the carburation, but also would need an
adjustment of the ignition of the kart, in fact different
conditions of pressure and temperature by changing the speed of
combustion, the heat transfer of the engine, and consequently also
if is proper the jetting, the exhaust temperatures
change, and therefore the curve of torque and power does not vary
simply its level in proportion to the density of air,
but it changes also its trend, and behold that all the decisions made before
may be biased.
How to intervene on the ignition timing of the kart track at
changing weather conditions to always obtain the
best engine performance and the torque curve best suited,
is therefore very important, but it is also extremely difficult,
in fact also if we've available the sensor of the exhaust gases temperature, and we
know on which values of temperature the engine operates at
better, you will never know if the temperature is high or low for fault of the
carburetion, or for the ignition timing of the kart that must be
changed.
Given this difficulty in practice rarely act
on ignition timing, but will compensate for variations in
speed of combustion and heat transfer, always acting
only on the carburization, this conventional practice by a point of
view of performance mitigates the problem, but often determines
problems of detonation, overheating, and in any event not
lets you really get the most out from your engine karts.
Apparently there would not be alternatives to this way
proceeding, if not to use the experience to avoid damage, and to play
on the wire with the carburetion, also because in the race there isn't the time to do tests with several ignition timing,
Fortunately, however, the technology can provide a great help, and
tell you with a good approximation to what happens to
combustion and heat transfer when the weather conditions change
and then tell you how to adjust the ignition timing accordingly.
These algorithms of calculation have been studied in the first place to
the electronic control units, in order to manage both the
carburation, both the ignition timing, the variation of pressure,
temperature and humidity, and then you get the most
from the engine.
In the kart and in the other 2-stroke engines used in other
competitions, not having an electronic control unit, these algorithms are
implemented in software that according to the specific
engine characteristics and the weather conditions tell you beforehand
how you must modify the ignition timing of the kart for the
new conditions, thus is possible to do manually what
would make the control unit in those conditions of pressure, temperature
and air humidity.
The use of these software allows to the mechanics to have
an opportunity hitherto impractical for the fine-tuning on track
of engine kart, namely, to optimize both the carburetion, both
the ignition timing of the kart, not being therefore more forced
to work only on a single parameter to compensate the deficits of the other.
This can lead to undoubted advantages both from the point of view to find
the maximum performance of the engine kart, both to reduce
drastically problems of detonation and overheating.
Continuing the reading you can start thinking of putting a
important step for the growth technique of your team and of your
job.
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