When Cpt. Edward Murphy coined the phrase "If anything can go wrong, it will" he had been troubleshooting an Air Force project when he found a transducer wired incorrectly. Murphy's Law could apply equally as well to stock ignition systems, which never fail to always fail at the most inopportune time. The frustrating scenario of a motor that cranks but doesn't fire was played out just recently at the FordMuscle shop when we tried to fire up our Streetwise 460 motor. After cursing our luck and yelling expletives at various parts of the vehicle, we traced the problem to an erratic spark from our budget Duraspark setup (see Streetwise 460, Part III.)

Keeping it Simple
In seeking out a replacement ignition system we had two major requirements in mind; performance and ease of installation. While the standard "red-box" multi-spark system is tried and true, we didn't want to hassle with finding a spot to mount the brick and then running, stripping, and crimping wires all around the engine compartment and under the dash. We wanted a simple clutter-free installation and only one D.U.I Distributorproduct seemed to offer this for Fords, the Davis Unified Ignition (D.U.I.) from Performance Distributors. We'd been familiar with this name from our Mustang projects, as their "Screamin' Demon" coils and coil packs are a huge hit for late model 5.0L and 4.6L engines. We were surprised to learn they had a drop-in, single wire, billet distributor for 385-series and 335-series Ford engines. They are actually offered in two styles, a Street/Strip unit with vacuum advance (shown) and a Race version with only mechanical advance.

At first glance, any blue-oval devotee will tell you this is a GM HEI (high energy ignition) distributor and may scold you for considering GM parts for your Ford. While it is indeed based on the classic GM design, Performance Distributors has re-engineered it from the ground up, making it more reliable and powerful. We're always of the opinion that you should run the best technology, regardless of who developed it first. In the 70's automakers re-designed their ignition systems to improve emissions by improving combustion and ensuring a compete charge burn, something not capable with existing points style distributors. Ford created the Duraspark system which uses a magnetic reluctor to switch the coil. GM went one step further and utilized a Hall-Effect sensor (see side bar) in their HEI design. Hall-Effect sensors offer better accuracy and reliability at high rpm. Performance Distributor's went the HEI route because founder Kelly Davis' experience in racing and ignition system design concluded the HEI systems to be a better starting point for designing ignitions for performance applications.

The D.U.I. distributor conveniently incorporates the three major ignition system components (spark module, inductance coil and distributor) into one simple and strong package. The coil and spark module are of course Performance Distributors' own re-engineered and improved designs which have better dwell times for increased coil saturation and fatter spark output as rpms rise. Performance Distributors tells us spark output is good to 9,000 rpms, something stock distributors are not capable of. In fact the D.U.I. is good beyond the scatter point of many aftermarket dizzys.

Custom Curved
It is rare, especially with the breadth of today's aftermarket products, that off-the-shelf parts can go together and be perfectly tuned for each other at the first turn of the key. As a result, more and more power- minded enthusiasts are seeking out custom shops to source carburetors, cams, headers and a host of other parts which are built to their engine and vehicle specifications. Distributors are no different. The amount of advance a distributor produces beyond initial timing is a function of the centrifugal and vacuum advance mechanisms within the distributor. If the rate at which timing advances is too fast, too slow, or if the total advance is incorrect for that specific engine, performance and fuel economy will suffer. On high compression or forced induction vehicles it goes without saying that too much timing can be detrimental to the motor. Performance Distributors has realized this and as a result curves each distributor specifically to your engine and vehicle specifications. It was a pleasant surprise while ordering our D.U.I. unit that we were asked to supply details regarding the motor, planned usage and rpm range, cam specifications and stall speed. What was delivered to us was a distributor which required no tweaking other than setting the initial advance.

(Installation and Dyno Testing)

In This Article:
We review and dyno test Performance Distributor's Davis Unified Ignition (DUI) distributor and LiveWire spark plug wires on our Project 460 motor.

How it Works
Hall-Effect Sensor Distributor

Named after physicist discoverer, Edwin Hall, a Hall Effect Sensor operates on the principle that when a piece of metal with current running through it is passed through a magnetic field it will generate a secondary voltage perpendicular to the metal. In a distributor, a current carrying silicone chip and magnet are set stationary facing each other. A vaned element passes between the two, breaking the magnetic field. This produces a very consistent and precise digital "square wave" voltage signal, which is then used by the ignition module to control current flow to the coil and subsequent spark to the cylinders. While a Hall-Effect sensor uses a magnet, it should not be confused with magnetic reluctance type distributors (such as a Duraspark) which utilize the small voltage "flux" created when a metal vane passes next to a magnet. These systems generate a weaker sine-wave signal which is prone to break-up as rpms rise.

The D.U.I's housing is CNC machined from billet aluminum for strength and good looks. Inside are two sets of bushings, one at each end, for drive shaft stability - this is key in maintaining spark accuracy at high rpms.

Under the cap and rotor is the precision Hall-Effect sensor and the aforementioned four-pin spark module. The Dyna-Mod module has increased dwell time for better coil saturation.

Mounted atop the wide-terminal cap is a 50,000 volt coil. While the D.U.I. coil is of higher output, it is the same shape as a stock GM HEI coil, making it easy to plug in a replacement in a pinch.

The distributor only requires a key-on 12V power source to run (our yellow wire here) , which truly makes it a one-wire system. A tach output terminal (gray wire in this photo) is provided as well. The other connections between the sensor and coil come pre-wired from the factory.



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