<VV> Cold plug/ Hot coil= what?

[Dave Thompson]

Thanks Frank,
That was a great explanation. 
So could someone answer this question? I run my Spyder with AC44F plugs,
.035 gap. They are listed as "mid range". Due to the lower 91 octane rating
of the fuel available to me here in So Cal. I have my timing retarded to
stop pinging. (I can't find the note right now to tell you how much). You
said that "The hot tip can also promote pinging."  I have a set of new
AC42F's in stock (listed as a cold plug). If I installed them, could I
advance my timing a bit and still not have pinging? Or are there a number of
other issues to contend with? 

Currently, the engine runs strong and I begin to get boost at about 1700 to
2000 RPM through all the gears (a little higher in 1st). The boost gauge
pegs on the boost side very quickly if I keep my foot in it.

My CHT indicates about 375 in the city and goes up to 400 on the highway. I
have never seen the temp over one needle's width above 400 indicated, even
on a 100F+ degree day. I know that the CHT gauge is not accurate to the
actual temp but it seems to me that stable indications show stable temps. I
have the lower shrouds and thermostats installed and working correctly.

I'm just looking for a few more horsepower through tuning (read timing
advance). 

I know I could add a knock sensor and such but my engine is basically stock
and I want to keep it that way.

Do I understand things wrong?

Dave Thompson
63 Spyder Vert
Westminster, CA

Frank wrote:

No, you're Jeff, I'm Confused...

Anyway, the heat range of a spark plug is related to the ability of the 
plug to shed heat, typically by the heat conductive path from the tip to 
the shell. The longer this path, the harder it is to get rid of the heat 
from the tip of the plug.

A "hot" plug has a long path, therefore a hotter running tip 
temperature. This would be helpful if the engine ran cold in the 
combustion chamber, like a short trip city car running a rich mixture.

A "cold" plug has the short thermal path, therefore the tip runs cooler. 
This would be helpful for a hot running combustion chamber, say a lean 
mixture condition, high compression, extended trips at high speed, etc.

A plug that is too hot for its application will show damaged porcelian, 
typically really white and bubbly. The hot tip can also promote pinging.

To know if increasing the part number increases the temp of the plug you 
must consult the manufacturers literature. Not all manufacturers do it 
the same way.

Frank DuVal

Jeff Wilson wrote:

>Someone educate me what the 'temparuture' of a plug really means. 
>How does this relate to gap of the plug and 'hottness' of the spark, and 
>the voltage produced by the coil, etc etc? 
>
>I'm sooooo confused.... 
>
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