[Supras] Spark plug wire choices

[Jeff Mohler]

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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