In a message dated 97-10-21 00:39:22 EDT, mgb.roadster@juno.com writes:
> I have always wondered about the thickness of spark plug wires. I have
> noticed they come in 7mm, 7.5mm and 8mm, and maybe more sizes. Is this
> the gauge of the wire? Why are there multiple sizes? Isn't bigger
> better (within reason)?
Larry:
The 7mm, 7.5mm, and 8mm numbers refer to the outside diameter of the
insulation, but the wire gauge is also larger as the diameter goes up.
On a stock MG, the coil primary draws less than 4 amps, and the secondary
produces around 20,000 volts. On some of the race cars, particularly drag
racers, the coil primary draws as much as 36 amps (that is not a typo - 36
amps!!!), with an output of 60,000 volts or more! The thicker insulation
helps to prevent flashover, or arcing, to ground, and also reduces the
potential for "cross-firing" - where the current in one wire is inductively
coupled over to an adjacent wire, causing two plugs to fire, rather than one.
It is not good for the correct plug to have to share the spark energy with
another, and it can be devastating to the engine if the wrong plug fires.
Keep in mind, the engines in the top dragsters produce in the neighborhood of
5000 horsepower! A bit more than an average LBC, even those with a V8! Of
course, our cars have to run for hours at a time, compared to 5 to 10 seconds
for the dragsters.
Also, along with the higher coil primary current and the higher secondary
voltage, the secondary will also produce more current. The large gauge wires
don't reduce the current as much as a standard wire.
Wires of this type can be bought with or without radio supression. Obviously,
the racers aren't listening to the radio, so the choose without.
While it is true that bigger is better, bigger is not always needed. For our
use, the larger wires should be considered as a comestic enhancement, rather
than a performance boost. The wires usually come in either red or yellow, and
they do look good! If you really want to get fancy, they can be found in
magenta, blue, green, orange, and other colors - bright colors - as well.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74
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