Basic inductive ignition boxes, such as Mallory's HyFire I, II, or III; Crane's HI-6S; and MSD's Blaster Ignition, take some load off the coil, do a better job managing dwell time and high current, and give the spark some extra punch. This typically translates into easier starts, smoother idling, and crisper throttle response.
More common are capacitive discharge ignition boxes with multiple-spark features. A CD box takes battery supply voltage, uses an internal transformer to step those 12 volts up to 500 volts or more, and stores that power in a capacitor. This voltage is stored at full strength so it's ready whenever the distributor sends a trigger signal. When boosted again through a matched performance coil, the resulting charge can be 30,000-45,000 volts riding the wires to your plugs throughout the entire rpm range. This hotter spark not only promotes quicker starts, a smoother idle, better throttle response, and fewer high-rpm misfires, but also lengthens point life (if you still have points). That's because the points now merely trigger the box, so they handle less current-typically less than 1 amp instead of 2-3 amps. Maintaining optimum point gap is also not as critical.
The multiple-spark feature found on most CD ignitions helps compensate for their one shortcoming: a shorter duration spark than inductive ignitions. This presents a problem primarily at lower rpm when the combustion process is slower and fuel mixture is typically richer. The solution is to fire the spark plug multiple times when the engine is below a certain rpm level-generally about 3,000-3,500 rpm. This is especially beneficial if your engine runs rough or rich at idle due to a lumpy cam or excessive carburetion--but we wouldn't know anything about that, now, would we?
The myriad ignition boxes available these days offer a wide range of other features like rev limiters and retard controls that allow timing adjustments in relation to supercharger/turbo boost or nitrous application. Most companies also offer digitally controlled ignition boxes and even PC-programmable boxes. You can do the research on what's best for you, but most street-oriented rods are well served with basic "6-Series" ignition boxes like MSD's 6A or 6AL, Crane's Hi-6, or Mallory's HyFire VI.
What's the point?"Hey, this is the 21st Century! What the heck am I doing fooling around with points?" Hey, we hear you and would like to stress that the upgrades we just discussed can do wonders for electronic ignitions, too. Meanwhile, let's talk about the many options for stoking your fire electronically.
Most domestic engines built since the mid-'70s, as well as most crate engines, came with electronic ignitions from the factory. GM's HEI distributor, with its integrated coil and easy one-wire hookup, has been a street rodding staple for decades. Likewise, Ford's Duraspark and TFI and Mopar's box-controlled electronic distributors are familiar to many rodders. They're all well suited for mild-milled rods and customs, and all can be easily upgraded with aftermarket coils, caps, modules, and control boxes.
Converting a breaker-point distributor to electronic operation is easier than you think thanks to the many available aftermarket kits. The Ignitor and Ignitor II conversion kits from Pertronix are very popular and can be had for a wide range of engines. Ignitor kits hook up with two wires, replacing the points with a Hall-effect-style pickup and reluctor wheel that work together to trigger the ignition. Crane's XR-i conversion for Fords and Chevys is even simpler-an electronic module replaces the points and uses the distributor's cam to create a trigger signal. It also has a built-in rev limiter. Mallory recently introduced a new E-Spark conversion as a lower-priced option to its long-running Unilite line. Like Unilites, E-Sparks use an optical trigger that's not speed sensitive (it doesn't need to reach a certain rpm to start triggering). Both are available for most Mallory distributors and a wide range of domestic points distributors.