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Spark plugs -- theory and practice
In the August 94 issue of european car there is a short article in the "Getting
Technical" section on spark plugs and some of the benefits/drawbacks of
different types of plugs.
The primary consultant in the article is Dr. Chris Jacobs, Phd, EE. Dr. Jacobs
is described in the article as "the brains of Jacobs Electronics".
Unfortunately, the article identifies him as a independent source of information
on spark plugs. Being the cynical guy that I am I take issue with a premise or
two in the article, but in general the info is good.
Generalizing a few points here: The amount of voltage required to jump a gap is
directly related to the amount of energy in a spark. The more energy in a
spark, the more energy available for combustion; therefore more power is
available from a given fuel/air mix (more complete combustion). The conclusion
would appear to be the higher the spark voltage, the better.
The article describes the primary drawback of high voltage plugs as misfires:
the ignition system (from coil to plug, inclusive) is often unable to reliably
produce a sufficiently high voltage to generate a spark on a regular basis at
high rpm.
According to the article here is where you gain your benefit from platinum
plugs: low arc-over voltage requirements (the amount of energy required to
spark) in platinum plugs reduce the amount of misfires in an engine with a weak
ignition system. The article then describes the various triple electrode or
crows foot plugs as mechanical attempts to due what the platinums do chemically:
reduce the arc-over requirement.
I'll agree with the article to here, with a disclaimer: If the plug gap were the
same, this would be true. Different gapping, different results. Long term
would also yield some side effects: plug life, etc.
Here is where the sales pitch starts kicking in in the article: "In Jacobs
Electronics' extensive testing of assorted spark plugs, we have noticed an
increase, on some occasions, with weak ignitions using specialty plugs. We have
never seen an advantage to using specialty plugs with the Energy Team, Omni-pak,
and especially with the Ultra Team ignition systems," Dr Jacobs explained.
I'll even buy this argument, but I will throw out a rhetorical, cynical
question: If something NEVER happens, how can it ESPECIALLY NEVER happen?
This discussion left out some of the other aspects of plugs: durability,
potential to foul, etc.
I'll cut to my point here: My stock ignition system (weak or not) does not
misfire with the platinum plugs, and I think I am achieving fairly complete
combustion (standing-by for correction). I do not feel I would gain much from
changing to something different. I have heard the copper plugs sometime suffer
from "spark blow-out". This could probably be described as a mis-fire. I feel
the potential/theoretical performance gain achieved from using a copper plug
would be offset by a higher likelihood of misfires. I could "fix" this problem
with an aftermarket ignition system, or I could not mess with a good thing.
Platinums cost more, but to me they are worth it.
Joe Yakubik