Editor Richard Kratz and J.R. Granatelli swapping coil packs on the GMS dyno.

Late Model Hemi Ignition Coil Dyno Comparison

Classic and late model Mopars couldn’t have different ignition systems if they tried. Back in the day high voltage spark was distributed to the spark plugs by a mechanical distributor. There was a single coil that generated the high voltage for all eight cylinders. A mechanical shaft spun by the camshaft rotated a rotor which sent the generated high voltage via an arc across an air gap to a distributor cap terminal. There the high voltage pulse traveled down a long wire to the spark plug. These high voltage ignition wires had to be thick and well insulated against heat and voltage leakage.

Late model cars use individual coils for each cylinder, usually referred to as “coil packs.” This “coil-on-plug” design requires that only low voltage be routed to each cylinder. Once the low voltage trigger signal reaches the coil pack, the signal is transformed up to a high voltage which only needs to travel a couple of inches from the coil to the spark plug.

The coil-on-plug system avoids the pitfalls of having high voltage travel long distance in vulnerable wires to the spark plugs. More importantly, the old distributor design only allows for spark advance/retard on a global scale for the car, any advance or retard occurs equally for all cylinders. The coil-on-plug design allows the engine control computer to adjust the spark curve on the fly for each cylinder individually (on some cars) thus maximizing efficiency which is important for fuel mileage and emissions control.

Old school factory single coil systems were not known for their amazing voltage output. A very common mod was to upgrade to a better quality aftermarket coil and ignition wires. With modern coil-on-plug systems, very few people both to upgrade their systems. As our testing proved, this is a shame as there is power to be found even in the late model system.

In theory, a higher voltage spark cannot gain horsepower per se. If the ignition system is working perfectly, meaning that every power stroke of every cycle for every cylinder is ignited by the plugs then there is nothing else to do, the fire is lit. In other words, the only way an ignition upgrade can gain horsepower is if there are misfires, some power strokes where the mixture isn’t ignited, or at least not fully ignited, in the cylinder. Put another way, ignition system upgrades generally can only gain back power that is being lost due to incomplete ignition occurring.