[Supras] Spark plug wire choices

[berniek at technicaldevelop.com]

Jeff:

    I'm just stating what has been a matter of experience.  Don't know if
you are pulling my leg, but I suspect you are not.

    If Christian is using a CD system at very high boost, the situation may
favor low resistance wires.  Jacobs makes both CD and multispark systems
(multispark is good at part throttle with lean mixtures, but offers no
advantage at WOT.  I know from experience).  But at one point with 10 PSI
boost before the BHG, I made up a solid core wire system for my Supra using
Packard solid core wire and "crimp-on"ends.  The car did not have the "dig"
that it did with carbon wires.  So I ordered new stock wires, and the
performance returned.  Just stating fact, without embellishment.

    Thanks for the sprockets.  Take care:

            Bernie


----- Original Message ----- 
From: "Jeff Mohler" <speedtoys.racing at gmail.com>
To: <berniek at technicaldevelop.com>
Cc: <wellner.christian at navy.mil>; <Supras at supras.com>
Sent: Thursday, July 27, 2006 9:30 PM
Subject: Re: [Supras] Spark plug wire choices


> Bernie:
>
> yer full of shit.
>
> We ALL know that BLUE wires with red lettering, really work best.
>
> ;)
>
>
> Especially synthetic ones.
>
> cam gears you will have on Tuesday.
>
>
> On 7/27/06, berniek at technicaldevelop.com <berniek at technicaldevelop.com>
wrote:
> > Dear Christian and list:
> >
> >     Over the course of many years, I've found that carbon core spark
plug wires consistently outperform solid or low resistance (or inductive)
wires.  This has been the case in cars owned since 1961, and appeared to be
particularly true with higher compression engines in cars like the 1965 GTO
and 1970 Firebird (still have, with Chevy BB engine).  It would follow that
turbocharged engines fall into the same category.
> >
> >     At first, this observation appears to run counter to what logic
dictates:  after all, shouldn't the stronger spark provided by low
resistance wiring produce more power?  The first crack in this reasoning
came about as a result of employment related factors in chemical engineering
in the mid '60's.  Articles about this from an expermental standpoint also
appeared in at least one of the hotrod magazines in the late '60's or early
'70's.  If you are old enough to remember when Roger Huntington wrote for
Popular Hot Rodding, it may have been him.
> >
> >     The primary consideration is one of air-fuel ionization time.  Just
like the treble control in a stereo system, the use of resistor-capacitor
"low pass filtering" of a sort appears to allow time for partial ionization
to occur before the voltage gradient across the spark gap rises high enough
to finally tear the last of the valence electrons from the mixture in the
vicinity of the plug gap.  That is when the spark occurs.  The
pre-ionization, in effect, is a "setup" for rapid combustion to occur in the
gap vicinity.  Ordinarily air and/or fuel ionization is the first step in
about five known steps in combustion, so getting a head start of sorts by
reduction of voltage risetime at the spark gap, and allowing some ionization
to occur first appears as the reason why more power is produced with carbon
than metallic wires.
> >
> >     The treble control in a stereo system fundamentally uses the
variable resistance of the treble control and fixed value capacitors to
limit signal risetime (fundamental consideration, most often more complex
from a design standpoint, but based upon the stated principle).  In the case
of spark plug wires, the capacitor is the distributed capacitance, along the
length of the wire, to "chassis " (engine) ground.  The resistance is
distributed in the wire.  Resistance distribution, to an extent, adds to
what is really a "transmission line" effect.  Transmission lines have a
characteristic "impedance" or current-voltage matching to the source and
load they serve.  That is one reason why the design of speaker cable such as
"Monster Cable" often makes a difference in stereo system sound, since the
cable impedance is lower (like the low impedance of speakers) than with
smaller conductors.
> >
> >     Inductive wires really do not offer enough inductance to be
meaningful regarding risetime limiting except for radio noise supression,
which implies a "filter frequency" (the inverse consideration of risetime)
much higher (or faster in risetime) than will allow pre-ionization of the
fuel-air mixture.
> >
> >     A secondary consideration involves the fact that once the spark
occurs, voltage across the spark plug gap falls to just tens of volts, or
maybe a few hundred volts in the case of high combustion chamber turbulence.
This is the reason that "stick" arc welding can be done, where welding
machines have open-circuit voltages of only 60-70 volts.  Once the arc is
struck by scratching the elecrode on the workpiece, the arc continues.  This
contrasts with the tens of thousands of volts required to break down an air
or air-fuel gap in the first place.  Further, once the spark plug arc occurs
for a few tens or hundreds of microseconds, the flame front has moved
outward, and continuation of the arc is of no consequence.  Resistance wires
do shorten the arc time, because of the energy dissipated in the wire
resistance, but it is of no consequence.  The "time constant" of the arc is
determined by the inductance of the coil secondary winding divided by the
wire resistance, so higher resistance means a somewhat shorter spark
duration.
> >
> >     I really hope this helps, as counter-intuitive as it seems.
> >
> >             BernieK
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