[Supras] Spark plug wire choices

[Dm19959 at aol.com]

Interesting. I had an ignition breakup problem around 18psi develop not too  
long ago. Changed plugs and coils with no change (mixture as well as all other 
 parameters were fine). I finally decided to try some different plug wires 
(have  always run stock wires, no not the ORIGINAL wires but stock Toyota). I 
went  ahead and made a set using MSD Spiral Core (solid) wire. Miss went away 
and idle  smoothed out quite a bit. I had fears of running the solid (RF 
interference) but  have had no ill effects. I did not go with the MSD "Super 
Conductor" wires as I  have a lot of the Spiral Core wire left over from "back in the 
day" and just had  to buy some boots and terminals plus it allowed me to 
tailor the lengths to  better suit my setup.
 
-Dean
 
 
 
In a message dated 7/27/2006 6:26:14 P.M. Pacific Daylight Time,  
berniek at technicaldevelop.com writes:

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
_______________________________________________
Supras  mailing  list
Supras at supras.com
http://supras.com/mailman/listinfo/supras_supras.com