Re: Cable question - spark plugs and wire - aaaargh
From: Bill Noble[SMTP:william_b_noble-at-email.msn-dot-com]
Reply To: Bill Noble
Sent: Monday, January 05, 1998 12:50 AM
To: Tesla List
Subject: Re: Cable question - spark plugs and wire - aaaargh
aaargh, I can't stand it anymore, so let me try to put an end to this
There are three types of conductors in spark plug wire:
1. stainless steel
3. carbon impregnated string.
The first two are equivalent, but some hot rod type wire uses stainless - it
claims it's better, but I doubt it. The last one is called "suppression
wire" or resistance wire, and it is used to reduce radio interference.
If you don't use resistance wire, then you have three alternatives:
1. live with the interference (not a problem on a car without a radio like
my '38 plymouth
2. use plugs with resistors in them - typically the plug will have an "r" in
its number. (On champion plugs, the R is the first letter. there are also
sheilded plugs, denoted by a "V" used on aircraft. Nothing in
3. use terminals with resistors in them - my 56 porsche and my 944 porsche
use resistance terminals.
there is a 4th alternative, and that is to use shielded cables, but it's
pretty expensive - as it is a set of wires for my 944 (that's a 4 cylinder
engine) costs $140, but as I recall the 911 uses shielded wires (at a cost
of about $300 for a set of wires if my memory serves).
According to my copy of th eBosh automotive handbook (second edition, 1986)
page 410, the spark plug arc "takes place at voltages up to 20 KV and above.
the spark plug is subjected to verh high electrical mechanical, chemical and
specifically thermal stresses. In a 4-stroke engine (compression ration
e=9, speed n=4500 rpm), the following gas temperatures and pressures occur
in the vicinity of the spark plug during each full load sycle (30 ms)
presuming normal outside temperatures:
end of suction stroke - 60 deg c, 0.9 bar
ignition point - 350 deg c, 9 bar
maximum values - 3000 deg c, 40 bar
end of power stroke - 1100 deg c, 4 bar.
"The center electrode and terminal stud are interconnected inside a high
grade special ceramic insulator (al2O3) by means of conductive sealing
material. this sealing material simultaneously acts as a gas seal, and can
also be designed as an interference-suyppression or burn off resistor.
"The insulator, which is glased on the connection end is atached to the
nickle plated steel shell by shrinkage and reversal of the rim. ...."
hope this helps clarify the issue.
From: Tesla List <tesla-at-pupman-dot-com>
To: 'Tesla List' <tesla-at-pupman-dot-com>
Date: Sunday, January 04, 1998 1:18 PM
Subject: Re: Cable question
>From: Edward V. Phillips[SMTP:ed-at-alumni.caltech.edu]
>Sent: Sunday, January 04, 1998 5:45 AM
>Subject: Re: Cable question
>"So the question is: is the resistance really supposed to be in the wire
>itself, or is there a resistor moulded into the end plug perhaps? Seems
>to me that if you wanted #14 wire with a constant non-neglegible
>resistance per linear foot, it would have to be made of something other
> IT IS! Some form of string-like material seemingly impregnated