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RE: Spark Plugs

To: Sally or Dick Taylor <tr6taylor@webtv.net>
Subject: RE: Spark Plugs
From: "Robert M. Lang" <lang@isis.mit.edu>
Date: Tue, 20 Nov 2001 09:47:44 -0500 (EST)
On Tue, 20 Nov 2001, Sally or Dick Taylor wrote:

> Eric---I wonder why it is, that the late model head with its lower
> compression would call for the colder (N9) plug? 

I'll take a guess and suggest that this is related to the retarded timing
settings for the later cars. I know the 74 had the timing set to 4 ATDC at
idle... and this makes the whole motor run hotter.

> This is the plug that
> caused premature fouling in some of the early  seventies engines. Do you
> remember the source that recommends this heat range for the 75-76?

Ummm... the owner's manual?

> Also, a "shorter" plug could expose the sharp corner in the head near
> the tip of each plug, creating a hot spot.

The shortness here is just the length of the tip, not the overall length
of the plug. All the N type Champions have 14mm threaded section that is
.750 inches long.

> Dick T.
> '73

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