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Here are some tips to help you use the spark plug
as part of the diagnostic tools to understand how
your engine is performing.
The following symptoms or conditions may have an
affect on the actual temperature of the spark plug.
The spark plug cannot create these conditions, but
it must be able to deal with all the levels of heat,
otherwise performance will suffer and engine damage
can occur:
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Air/Fuel Mixtures seriously affect engine
performance and spark plug temperatures.
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Rich air/fuel mixtures cause tip temperature
to drop, causing fouling and poor drivability.
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Lean air/fuel mixtures cause plug tip and cylinder
temperatures to increase resulting in pre-ignition,
detonation, and possibly serious spark plug and
internal engine damage. |
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It is important to read spark plugs many times
during the tuning process to achieve optimum air/fuel
mixture. Computer-controlled engine applications
do a very good job of this with various sensors
that report back to the ECM. |
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| Higher Compression Ratios and Forced Induction
will elevate spark plug tip and in-cylinder temperatures.
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Compression can be increased by performing any
one of the following modifications:
a) reducing combustion chamber volume (i.e.: domed
pistons, smaller chamber heads, milling heads,
etc.)
b) adding forced induction (Nitrous, Turbo-charging,
Supercharging)
c) camshaft change |
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As compression increases, a colder heat range
plug is required, as well as higher octane fuel.
Paying careful attention to ignition timing and
air/fuel ratios are also necessary. |
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| Advanced Ignition Timing |
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Advancing timing by 10¯ causes plug temperature
to increase by approximately 70¯C to 100¯C. |
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| Engine Speed and Load |
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Increases in firing-end temperatures are proportional
to engine speed and load. When traveling at a
constant high rate of speed, or carrying/pushing
very heavy loads, a colder heat range spark plug
should be installed. |
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The heavier your vehicle or greater the amount
of work the engine sees (racing applications,
construction trucks, vans, RVs & motorhomes, etc.),
the more critical this becomes. |
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| Ambient Air Temperature |
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As air temperature falls, air density per unit
volume increases, resulting in leaner air/fuel
mixtures. This also creates higher cylinder pressures
and temperatures that causes an increase in the
spark plug's tip temperature. Fuel delivery should
be increased. |
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As temperature increases, air density decreases,
as does intake volume. Fuel delivery should be
decreased. |
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| Humidity: As humidity increases, air volume
decreases. |
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The result is lower combustion pressures and
temperatures, causing a decrease in the spark
plug's temperature and a reduction in available
power. Air/Fuel mixture should be leaner, depending
on ambient air temperature. |
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| Barometric Pressure and Altitude Affects the
spark plug's temperature. |
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The higher the altitude, the lower the cylinder
pressure becomes. |
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As the cylinder temperature decreases, so does
the tip temperature. |
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Many tuners attempt to "chase" tuning by changing
spark plug heat ranges. |
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The real answer is to play with the jetting
or air/fuel mixtures in an effort to put more
air back in the engine. |
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