Engine Coil Packs

Nearly all of our older cars have a single coil unless there has been an engine swap. Years ago we could get higher RPM’s by using an expensive dual-ignition system, but why is that? We’ll answer that question later. 

Have you noticed on your new car, each cylinder has it’s own coil mounted on top of the engine? These are coil packs. Let’s examine exactly what an automotive “coil” is, electrically speaking. 

It’s not really a coil at all, but a step-up auto-transformer where the primary and secondary are intertwined. The coil is fed a chopped 12VDC from the electronic distributor and steps the 12 volts up to a minimum 20K volts so it can jump the gap at the spark plugs. Why chop the 12 volts? Because a straight DC will be stopped dead and never pass on to the secondary of any transformer.


You have probably heard “hammering” in a water delivery system and that is caused by the water flow hitting a dead stop then sloshing back. A similar phenomenon occurs with coil electrical current flow, but is referred to as back EMF or back Electro-Motive Force. In a water flow system, the greater the flow, the greater the noise and possible damage. With electrical current flow, the greater the flow, the higher the back EMF when switched and can cause damage to the components. High amounts of back EMF will delay fast switching  from one spark plug to another and cause missing at high RPM’s. A hot coil can be counterproductive for this reason.

– Submitted by Chuck T.