But the heat range of the plug is only a function of the heat transfer rate of
the insulator. Hotter plugs have a longer path from the tip to the metal body
which transfers the heat to the head. So the tip of a hotter plug wood
maintain a higher temperature. However, any plug capable of igniting
combustion will create the same reaction in the combustion chamber and deliver
the same amount of power. A hotter plug may have less of a tendency to foul
if this is a problem.

Short Wave Sportfishing wrote:

On Wed, 25 Feb 2004 02:01:22 GMT, Jim Kelly wrote:

I am questioning your assertion that "combustion is strictly the pervue
of how hot the spark is." I contend that that it is necessary to
increase the fuel to air ratio on a cold engine because the engine is not
imparting enough heat to the mix to create a combustible mix regardless
of the heat range of the plug. Therefore, engine temperature has a
direct effect on combustion.

I can agree with that. However, combustion has to be initiated by the
spark. The fact that a cylinder is operating at certain temperature
only assures that the fuel/air mix on entering the chamber is fairly
evenly dispursed. The source of ignition is still the spark. A
hotter spark means that more energy is imparted to the explosive
mixture resulting in a cleaner burn with more energy transfer. The
gas expansion rate is better because the burn is initiated quicker.

Additionally, a hotter plug in a cold normally aspirated engine means
that one can use less choke on starting. Faster start, faster warm
up.

Later,

Tom
S. Woodstock, CT
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Basic Fishing Program:

10 - Fish
20 - Eat
30 - Sleep
40 - Goto 10