Subject: RE: hot spark plugs
Author: Greg Bender
Date: Apr 20, 2005, 8:54 AM
Post ID: 1718733370
Hi Mike,
I found this explanation on the NGK website:
Heat range
The term spark plug heat range refers to the speed with which the plug
can transfer heat from the combustion chamber to the engine head.
Whether the plug is to be installed in a boat, lawnmower or racecar, it
has been found the optimum combustion chamber temperature for gasoline
engines is between 500�C-850�C. When it is within that range it is cool
enough to avoid pre-ignition and plug tip overheating (which can cause
engine damage), while still hot enough to burn off combustion deposits
which cause fouling.
The spark plug can help maintain the optimum combustion chamber
temperature. The primary method used to do this is by altering the
internal length of the core nose, in addition, the alloy compositions in
the electrodes can be changed. This means you may not be able to
visually tell a difference between heat ranges. When a spark plug is
referred to as a �cold plug�, it is one that transfers heat rapidly from
the firing tip into the engine head, which keeps the firing tip cooler.
A �hot plug� has a much slower rate of heat transfer, which keeps the
firing tip hotter.
An unaltered engine will run within the optimum operating range straight
from the manufacturer, but if you make modifications such as a turbo,
supercharger, increase compression, timing changes, use of alternate
racing fuels, or sustained use of nitrous oxide, these can alter the
plug tip temperature and may necessitate a colder plug. A rule of thumb
is, one heat range colder per modification or one heat range colder for
every 75-100hp you increase. In identical spark plug types, the
difference from one full heat range to the next is the ability to remove
70�C to 100�C from the combustion chamber.
The heat range numbers used by spark plug manufacturers are not
universal, by that we mean, a 10 heat range in Champion is not the same
as a 10 heat range in NGK nor the same in Autolite. Some manufacturers
numbering systems are opposite the other, for domestic manufacturers
(Champion, Autolite, Splitfire), the higher the number, the hotter the
plug. For Japanese manufacturers (NGK, Denso), the higher the number,
the colder the plug.
Do not make spark plug changes at the same time as another engine
modification such as injection, carburetion or timing changes as in the
event of poor results, it can lead to misleading and inaccurate
conclusions (an exception would be when the alternate plugs came as part
of a single precalibrated upgrade kit). When making spark plug heat
range changes, it is better to err on the side of too cold a plug. The
worst thing that can happen from too cold a plug is a fouled spark plug,
too hot a spark plug can cause severe engine damage
Regards,
Greg Bender
1971 Ambassador
2000 Quota
http://www.thisoldtractor.com/gtbender
Florida MGNOC website
http://www.thisoldtractor.com/fl_mgnoc
Minnesota MGNOC website
http://www.thisoldtractor.com/mn_mgnoc