On Wed, 04 Jun 1997 22:51:46 -0500 Rick Jennings <ijsceva@kcnet.com>
writes:
>What determines if a plug is "Hotter" or "Colder" then the standard
>plug?
>
>
A spark plugs heat range is determined by the relative length of the path
heat must travel along the ceramic nose insulator before reaching the
metal shell and thence to the head.
"hotter" plugs have a longer thermal path, thus the insulator will run
at a higher temp than a "cold" plug with a relatively shorter path.
BTW, there isn't a magic number to determine the correct heat range of a
plug, and although the various manufacturers will list their Z-123 plug
as the replacement for the competitors SGF-87A plug, the heat range will
probably be slightly different.
And the required heat range of a spark plug for a given engine will
vary with the state of tune (stock or hot-rodded), type of driving, fuel
used, climatic conditions (to a minor extent), and most of all by the
weight of the drivers right foot!
When all's said and done, the best bet is to follow the owners manual
recommendation for plug equivalent, and then careful inspection at
regular intervals will reveal whether a colder or hotter plug is called
for.
Sorry to ramble on, but this late at night (12:05) I tend to get a little
loose jawed
Rick Morrison
72 MGBGT
74 Midget
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