In a message dated 6/26/04 1:01:49 PM Eastern Daylight Time,
spamiam@comcast.net writes:
<< Well, I am really confused.>>
First what a ballast resistor does:
For a ignition coil to have enough zip at high speeds, the primary side must
have a low resistance. At high speeds the points are closed for a short
period of time so the only way to build a strong magnetic field is high current
(
low resistance)
At low speeds, the points are closed for a longer period of time allowing the
magnetic field to build. We can build a field over a longer period of time
with lower current. This reduced current makes for longer point life.
In order to reduce the curent, we insert a balast resistor. The secret to a
balast resistor is that it changes to a higher resistance at high current
flow. It is self limiting so you can think of it as a regulator for the
ignition.
Some electronic ignitions ( GM HEI , Ford TFI ) use a current sensor built
into the module to limit current. Early Ford Duraspark and Chrysler electronic
ignition use a balast resistor/wire.
Balast resistors are made from Nichrome wire ( like a toaster element ) Ford
and GM had long used a balast wire in the harness, Chrysler used a white
ceramic resistor. There are a few different resistances and mountings. In
theory
things should be tuned using extensive testing, but in practice a generic
resistor should work fine. Be sure to contact Pertronix for a recommendation
for
total resistance, supposedly the ig module is sensitive to too low of a total
resistance.
<< It comes in the
mail a few days later and it is a 1.5 ohm coil as well!!!! The instructions
inside gave a little more info. It says that the coil can be used for RACING
applications on non-ballasted 4 cyl cars, but that for street purposes the
ballast resistor should be left in place. Well, I have no ballast resistor.
>>
For a racing application, the engine is running at high RPM most of the time
and tends to have regular point adjustment, in this case a balast resistor is
not needed.
<< I guess that I should use a 1.5 ohm resistor to get the overall
resistance to 3 ohms. Is that true?>>
I'd have to dig in some old ignition books, but this sounds reasonable.
<< What model car should I ask for a resistor at the local NAPA? The speed
shop has seemingly expensive ($11) resistors in 0.85 and 5 ohms, maybe a 2 ohm
as well.>>
Is this $ 11 resistor a single unit with 4 prongs? If so it sounds like a
73 to ~ 80 Chysler electronic ig resistor. Early Chrysler used the .85 ohm
side for the coil and the 5 ohm side for the ig box. Later Chrysler ~ 80 to 85
used a single 2 prong .85 ish resistor.
<< I would think I could get it cheaper by not having it for "performance"
applications.
Try a resistor for a 84 Dodge 1/2 ton pickup with a 318 V8. This will have 2
prongs.
Harold
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