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 product
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.
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)
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.