8. What coil is recommended for the Atomic 4?

Most coils with an internal resistance of 3 to 4 ohms should work very well in the Atomic 4.

In the unlikely event that your boat has had an external ballast resistor installed in its primary ignition circuit (somewhere between the ignition switch and the coil), you should select a coil with a lower internal resistance (approximately 1.5 ohms). The ballast resistor is a rather large porcelain device measuring about 4” long by 3/4” square, and it provides the additional 1.5 to 2 ohms necessary to bring the resistance within the primary circuit back up to 3 to 4 ohms. Coils which have a ballast resistor providing some of the required resistance externally tend to operate a bit cooler than coils with internal resistance. We have always been assured by manufacturers, however, that coils are designed to withstand the additional heat of internal resistance.

Manufacturers also point out that traditional metal-covered, oil filled coils tend to transfer heat somewhat more efficiently than solid epoxy coils. The fact that oil filled coils may feel quite hot to the touch is clear evidence that they are indeed transferring a lot of heat to the atmosphere (and to your fingers).

Unless coils are subjected to extremely high heat, physical damage, or oil leaks, they should have a life expectancy of many years. In many cases, coils last practically indefinitely. Some folks from very hot climates report that they have been able to improve their coil life somewhat by moving them outside of their very hot engine compartments. Prior to relocating their coils, they would have to replace them every year or two.

The increased dwell time provided by electronic ignition systems (approximately twice that of conventional systems) can cause coils to run somewhat hotter than those on engines with points and condensers. However, we have no evidence from our experience to indicate that coils used in electronic ignition systems fail significantly faster than those in conventional systems, nor do we have any indication that any good oil-filled coil (with at least 3 ohms internal resistance) will not work satisfactorily with electronic ignition systems. - Updated: November 4, 2003