That's it in a nutshell. The big advantage of metals like platinum,
palladium and iridium is their high melting point. You need a sharp edge on
the electrode to get a spark easily--it's the opposite of the rounded domes
of Vandegraff electrostatic generators that spread their charge evenly and
don't spark until there is a huge charge. If the metal melts a little from
the heat the edges round out. Common plugs have larger electrodes to conduct
the heat away. Platinums have small electrodes which inherently condense the
charge and spark easily. Iridium plugs have tiny electrodes that take a very
high temperature in stride.
The big deal in racing plugs is the fit the heat range you want and have
less taper to the ceramic which makes them colder on the tip. They don't
self-clean as well as standard plugs.
-----Original Message-----
From: owner-fot@Autox.Team.Net [mailto:owner-fot@Autox.Team.Net] On Behalf
Of Jim
Sent: Tuesday, October 26, 2004 6:48 AM
To: Barr, Scott
Cc: fot@Autox.Team.Net
Subject: RE: Interesting message
Scott,
I haven't looked for any online explanations for plug ratings, but I can
give a thumbnail answer.
In proper operation, a spark plug is not supposed to ignite the fuel-air mix
until it "sparks". In an ideal situation the flame is started at just the
optimum time and progresses quickly.
What can happen is that if it's a "hotter" plug than the application needs
then the ceramic and the electrodes get hot enough to ignite the mix
prematurely, acting like the glow plug in a diesel.
How do you make a spark plug cooler (at time of manufacture, of course)??
The spark plug is cooled by heat transfer from the ceramic to the metal
portion that threads into the cylinder head. So by changing the geometry of
the plug ceramic the manufacturers can tweak how quickly the plug cools
- in a relative sense- or how much heat they retain between firing cycles.
If you could cross section a "hot" plug you'd see the ceramic is a long thin
cone with the contact point to the metal far up the spark plug body.
A "cooler" plug has more ceramic and contacts down closer to the electrode
end.
In the car, if the plug is too hot you'll tend to get pre-ignition under
extreme conditions (pinging/pinking) which will do all kinds of neat damage.
If the plug is too cool it won't burn off the carbon buildup and eventually
foul. A perfect plug is one that is cool enough to not ping under full
load, but good enough to keep firing under cooler conditions.
HTH
Cheers,
Jim
Dallas TX
> <<the best race plug ever made.>>
>
> OK, I'll bite -- so what makes a plug a good "race plug"? The spark
> plugs (like a large, but decreasing, number of parts of our cars) have
> always been a mystery to me. What makes one hotter and one cooler?
> What do you see on the end of the plug that tells you whether you need
> hotter or cooler? Are there any recommended reading resources out
> there?
>
> Scott (B.)
>
> -----Original Message-----
> From: owner-fot@Autox.Team.Net [mailto:owner-fot@Autox.Team.Net]On
> Behalf Of Ted Schumacher
> Sent: Tuesday, October 26, 2004 7:16 AM
> To: Herald948@aol.com
> Cc: fot@Autox.Team.Net
> Subject: Re: Interesting message
>
>
> Andy, we still have Champion gold paladium plugs in stock. Probably
> the best race plug ever made. Plug numbers end in "G" to denote the
> gold paladium. A real race only plug. Ted
>
> Herald948@aol.com wrote:
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