I have a 1954 Ford with a 272 Y-block. Before I got it the previous owner had added triple carbs, dual pipes, and a PerTronix point replacement kit. The coil was a standard 12V replacement and there is a ballast resistor in the primary circuit. The engine ran great until recently; it became hard to start and finally wouldn’t start at all. Of course this happened at a cruise night where everyone could watch while I tried unsuccessfully to get it started.
Fortunately one of the guys with me had a spare coil with him, however it is from a different manufacturer and a completely different design. My question is, what is the difference between coils? I know there are so-called “hot” coils than put out more voltage than others and it would seem the hotter the coil the better, but how do I pick the proper replacement?
Via the Internet
In simple terms coils are rated by their primary resistance—less resistance in the primary windings of the coil allows more current to flow, which makes a stronger magnetic field. When the points open (or the electronic device that controls current flow shuts off) the magnetic field collapses and makes a spark in the secondary windings. It stands to reason that more current in the primary is a good thing, however the current flow is limited by the ability of the points, or the electronics in place, to handle it. Too little resistance means too much current flow, which can burn up points and damage electronic components.
For specific recommendations we contacted our pal, Don Lindfors, at PerTronix to get the straight story on coils. As he explains, PerTronix offers three oil-filled, canister-style coils and they are identified by the ignition system they are suited for:
The Flame Thrower 40,000V coils have internal resistance rated at 1.5 or 3.0 ohms. The 3.0-ohm coil should be used on PerTronix Ignitors installed on four- and six-cylinder engines while 1.5-ohm coils should be used for eight-cylinder applications. These coils can be used on virtually any inductive (non-capacitive discharge) ignition system.
Flame Thrower II coils have lower resistance, 0.6 ohms for use with Ignitor II ignition systems as well as many other high-energy ignitions. The low resistance helps to produce up to 45,000 V. This higher voltage allows larger spark plug gaps for added power and better fuel economy.
Flame-Thrower III coils were developed for use with the new Ignitor III electronics. The extremely low resistance of 0.32 ohms results in 45,000 V and a coil that charges to peak, current typically 30-70 percent faster the other coils. It should be noted that these coils are compatible with Ignitor III electronics only.
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