Coils & Things ©By: John T. Blair (WA4OHZ) 1133 Chatmoss Dr., Va. Beach, Va. 23464; (757) 495-8229
Originally written: circa 1999
This is published with permission from Chris.
John
Date: Wed, 26 Aug 1998 14:58:21
A coil is a coil is a coil. There seems to be thought that one coil is good
for vintage and another for current generation. This is simply not true.
However, it is important to match the coil to the balance of the ignition
circuit.
In the old days (vintage cars) coils were triggered by mechanical points.
Points are nothing more than a switch, opened and closed in sync with the
rotation of the distributor shaft. Points are prone to erosion of their
electrical contact surfaces. To combat this, series resistors were
introduced in the circuit to cut the voltage to the coil. Most cars of this
era have bypass circuits that provide full voltage to the coil during
cranking.
As Lewis pointed out, you can bypass the ballast and get a hotter spark all
the time on a resistor ignition circuit. Points are cheap, go for it.
On a breakerless ignition there are no points and there should be no need to
cut the voltage to the coil, ever. This applies equally to OEM and
aftermarket setups. I run a aftermarket hall effect unit in lieu of points
in a 1968 V4 distributor. It allows me to run any sort of coil I want with
no detrimental effects.
So whats the difference between black, blue, and red coils. The amount of
punch and the presence of an internal ballast. Black and red coils have no
internal ballast, and blue coils have one.
Coils are simple multipliers, feed them 12 volts and some multiple of 12
will come out. Coils typically come in powers like 100, 150, or 200, hotter
coils have higher multipliers.
Another performance trick is to feed the coil something higher than 12 volts
on the input side. A coil with 100 power will provide 12,000 volts out with
a 12 volt input but the same coil will produce 40,000 volts if you hit it
with 40 volts in. This is what (in part) an MSD unit does.
The problem is not all coils are up to the challenge of generating 40,000 or
more volts. They lack the insulation and the ability to dissipate the
increased heat. Performance coils are oil or epoxy filled.
Remember the old adage that a chain is only as strong as its weakest link.
This certainly holds true in an ignition circuit. The plugs and wires are
much more stressed carrying 40,000 volts than 12,000.
Higher potential (voltage) also allows for a greater spark plug gap. A
larger gap generates a bigger spark which in turn does a better job lighting
the charge (or so the propaganda says).
Compression is the adversary of spark propagation. The greater the
compression, the harder it is for the spark to jump the plug gap. So it is
customary to provide for a hotter spark when increasing compression rates
(this would hold for NA and Turbo cars).
Choosing a coil is therefor not as simply as it might initially appear.
Chris
To email me with comments or
questions.
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