Updating a breaker point ignition to Ford’s breakerless Duraspark II ignition is a simple plug and play operation. It requires a distributor, a wiring harness (Painless Wiring # 30812), a Duraspark II ignition module (blue strain relief, Motorcraft # DY-184 or SMP # LX-203) and a Duraspark II coil (Motorcraft # DG-314 or SMP # FD-476). Source the Duraspark distributor from any 1977 through 1982 351M, 400, or 460 Ford V8.
The Duraspark II ignition operated similar to a breaker point ignition, i.e. the dwell was fixed, thus coil charging time varied with engine speed. But it was designed to generate more spark energy. It utilized only 1.10Ω ballast resistance and only 1.17Ω coil primary resistance, yet the coil's secondary resistance was increased to 8,500Ω. Plug gaps were set at 0.050 inch. Breakerless electronic ignitions were designed to stay “in-tune” longer, and to ignite mixtures that breaker point ignitions were incapable of igniting. The engine starts quicker, runs smoother, and has better low rpm power. Power improves at all engine speeds. The ignition is an improvement over any breaker point ignition, including a dual point ignition. There are no points to adjust, thus maintenance is reduced. The Ford ignition is also more reliable than any aftermarket ignition.
The Duraspark I ignition was a several times more expensive high output ignition installed in all V8 powered California vehicles in 1977 and in 302 V8 powered California vehicles during 1978 and 1979. It was designed to reliably ignite mixtures the Duraspark II ignition could not, and thus reduce misfires.
Duraspark I utilized a special coil having a very low 0.70Ω primary winding resistance which operated without a ballast resistance; therefore current flow in the coil’s primary windings was substantially increased. The core of the coil was designed to accept a much higher magnetic charge from the increased current flowing in the primary windings, thus producing a substantially higher voltage to the spark plugs. Plug gaps were set at 0.060 inch. The higher magnetic charge also allowed the coil to reach "full charge" more rapidly.
To control coil charging Duraspark I employed “dynamic dwell” circuitry. Dwell was continuously adjusted electronically based on current flow in the coil's primary circuit, independent of engine speed. This prevented over charging or under charging the coil throughout the motor’s rpm range. Dwell varied with respect to the degrees of crankshaft rotation but remained relatively constant with respect to actual coil charging time; as a result the coil was properly charged throughout the engine's operating range giving the ignition a consistent spark regardless of rpm.
All of Ford’s ignitions have been designed to operate like this since the TFI ignition was introduced in 1983. The Duraspark I ignition was the predecessor, the first on the block.
Duraspark I requires a different module (red strain relief, Motorcraft # DY-204 or SMP # LX-210) and a different coil (Motorcraft # DG-316 or SMP # FD-477). A Duraspark I wiring harness is not available, but the Duraspark II harness and the Duraspark I coil can be modified so everything plugs together properly.
Modifying a Duraspark II wiring harness for Duraspark I applications
- Swap the positions of the orange and green wires at the 4 pin connector.
- Remove the Duraspark II “key tab” from the 4 pin connector. A razor blade or box cutter work well for this job.
- Do not utilize any ballast resistors or resistance wire. The ignition module and coil need a full 12 volt supply.
- Modify the Duraspark I coil tower to allow the Duraspark II “horse shoe connector” to slip-on the Duraspark I coil. When you try to slip the connector on the coil it will be obvious which “tab” needs to be removed. A Dremel tool works well for this job.
The Duraspark II module can be mixed and matched with other coils, if that's where your head is at. People have done so for decades.
The Duraspark I module however, employing dynamic dwell, is designed to be used with a specific coil. You wouldn't want to mix and match parts with that system. And the Duraspark I coil has such low primary resistance that it shouldn't be used without the Duraspark I module to charge it properly. Don't let the round can packaging fool you, it's a high tech, powerful coil ... engineered before the days of "designer coils".
Both Duraspark I and II modules are as reliable as claw hammers. If I had to put a number on them, based on experience I'd say they're good for 100,000 miles. One caveat however, I personally buy '70s ignition parts new old stock made in either the USA or Mexico, and I avoid newer stuff made in Asia.