With the energy to create a fat blue spark across a wider spark plug gap a good “breakerless” electronic ignition can ignite fuel air mixtures that a breaker point ignition never could. This reduces “misfires” which has several benefits including easier and faster starting, more low rpm torque, more horsepower at all rpm, fewer emissions and better fuel economy. The engine’s maintenance is reduced as there are no breaker points requiring periodic adjustment. Reducing misfires also makes an engine run smoother (less vibration) therefore a good electronic ignition reduces vibration and harshness. And since the forces causing vibration are destructive forces, reducing vibration means those destructive forces are reduced, improving the durability of the engine.
A Ford Duraspark ignition is reliable and tune-up parts are readily available. A Ford ignition will be preferred by those who favor factory parts over aftermarket parts. Although several Duraspark ignitions were manufactured, only two are of interest. The modules are visually identified and referred to by the color of the wiring “strain relief” where the wires exit the module. The two modules of interest are the “common application” Duraspark II version which has a blue “strain relief” and the high output Duraspark I version which has a red “strain relief”.
Choose a Duraspark II ignition for engines rev limited at 6200 rpm; the Duraspark II ignition is a fixed dwell ignition, it operates identical to breaker point ignitions in that aspect. Fixed dwell ignitions properly charge the coil over a narrow band of engine speed at mid-rpm; below that the coil is over-charged and above that the coil is under-charged. The ignition operates with 1.10Ω ballast resistance and 1.17Ω coil primary resistance; thus the coil operates on 7 volts. Spark plugs are gapped at 0.050 inch for Duraspark II.
Choose the high-output Duraspark I ignition for engines rev limited at higher rpm or if you prefer the best performing ignition regardless of the rev-limit. The Duraspark I coil operates at full voltage (i.e. no ballast resistance) and the coil has a very low 0.70Ω primary resistance. The charging of the coil is controlled by the ignition module which varies dwell angle based upon engine speed so that the coil charging “time” remains constant; this is known as dynamic dwell. Dynamic dwell charges the coil properly at all engine speeds, including high rpm; the coil is never over-charged or under-charged. Spark plugs are gapped at 0.060 inch for Duraspark I.