5.0 Mustang & Super FordsHow To Interior Electrical
Crane HI-6R Capacitive-Discharge Ignition - Sparking Performance
Installing A Crane HI-6R Capacitive-Discharge Ignition
Horse Sense: The HI-6 uses a sequential firing program to equalize cylinder firing at the rev limit. All cylinders will be fired equally in rotation, reducing fuel loading and plug fouling. Sequential firing is also said to minimize harmonics and vibration that can stress engine/drivetrain components.
If you have a 5.0 and plan on a turbo- or supercharger, you might also plan on upgrading to a capacitive-discharge ignition, since the factory spark can't overcome the resistance of high cylinder pressure at high rpm. Similarly, nitrous or increased compression ratios can also overwhelm the factory Thick Film Ignition firepower.
Though fine in stock applications, the major limitation of an inductive-discharge ignition, like the TFI and practically all other OEM ignition systems, is the relatively (continued on p. 183) low voltage applied to the primary side of the coil, and the subsequent lengthy time required to charge up the secondary side-the side that fires the spark plugs. Combine this slow recycle time with the increased current demands of high cylinder pressure, and it's easy to see why the factory setup can't be relied upon to light off those dense mixtures under high-rev boost. No fire, no fun.
As the name suggests, aftermarket capacitive-discharge ignitions, such as the Crane Fireball HI-6R we're installing here, use a discharge capacitor fed by a high-voltage power supply (450 volts, in the case of the HI-6) to energize the coil secondary, resulting in a very high-voltage spark-one that will not be extinguished under high cylinder pressure. And since the capacitor can recharge almost instantaneously, a CD ignition can, at lower rpm, fire multiple sparks for each ignition event. On the HI-6R, the number of sparks fired is varied to maintain a total spark duration of 20 crankshaft degrees, assuring thorough combustion for maximum response and efficiency. Above 3,000 rpm, the system reverts to a single spark-but one with many times the current of a stock system.
When you get it home and tear open the box, the number of wires lurking inside might at first seem intimidating, but installation of a CD ignition is actually quite straight-forward. Of course, that's easy for us to say, as we enlisted the capable crew at Da Silva Racing to do the hard work while we just messed with a camera and lights. On a difficulty scale of 10, we'd have to rate this job as about a 2. Just be patient, and eyeball our photos and captions-and the instructions, of course.