> I recently purchased a new Mallory Unilite distributor with vacuum advance,
> their coil, a recurve kit and a new ballast resistor from them. I was looking
> for a stock-ish distributor that did not require an additional external box
> (like the MSD).
Be aware the Mallory Unilite module is just a points eliminator so don't
try to run a wide plug gap. If you want a high energy spark, you'll need
a capacitive discharge box of some sort (MSD-6AL, Mallory HyFire, Crane,
etc.). Once you've got it installed, test the spark with one of those
inexpensive spark testers (look like a a spark plug with a clear glass body
and a grounding clip).
If you run a spark box, the wiring is different but Mallory has detail
diagrams for those. A ballast or resistor wire is not needed when using
an external box like an MSD-6AL since all the current for the coil goes
through the box rather than the module. When used with an external box,
a Unilite module will last almost forever because very little current goes
through it. MSD suggests you leave the ballast or resistor wire in place
so it can be hooked back up should the MSD box fail. I had that happen
once and just used the MSD supplied jumper and fired it up and drove home.
Now I carry a spare MSD.
There's a maximum voltage at the photoelectic eye (7 to 9 volts) that's safe.
Above that, the Unilite will work just fine but it will eventually fail.
Also, don't run solid core wires with the Unilite. They will also eventually
kill the module. Apparently the coil wire is the worst culprit and some coils
can leak back to the module when the ignition is switched off. The module
will pick up noise and produce a poor trigger signal if the wires aren't
suppressed. Also, the module is cooled by heat transfer to the aluminum
housing. There is a thin layer of white dielectric grease between the module
and the housing that helps heat transfer. The grease will eventually dry out
so it's a good idea to put in a fresh layer after a number of years.
The Unilite uses a three wire hook up. The brown wire is grounded to the
engine. Make sure you also have a good ground cable/strap between the engine
and the body. Do not ground the brown wire from the module directly to the
frame or battery. If you do, the brown wire will become a ground for the
starter during cranking which will melt the brown wire and take out the
module. The green wire connects to the negative side of the coil. The red
wire can connect to the positive side of the coil but it's better to connect
it to the high side (12 volt) of the ballast resistor. The ballast or
resistor wire is there to limit the current through the coil and the green
wire. The red wire prefers to see full battery voltage. If you connect
the red wire to the positive side of the coil (which is also the low side of
the ballast) the engine may not start as easy especially if the battery is
low. If your car has a resistor wire rather than a ballast, you can either
hook the red wire to the positive side of the coil, or better yet, find a
place to hook it that will feed the red wire full battery voltage whenever
the key is on.
Don't use solid core plug wires with any electronic igntion.
If you weld on the car, disconnect the module before doing so.
Still with me? Once the wiring is verified, you should probably check the
advance curve with a dial back timing light. Do you have the stepped Mallory
key that's used to set the stops? You may want to pick up a kit to curve the
distributor. The mechanical advance mechanism is buried below the optical
pick up. To alter the curve, you need to change springs, as well as adjust
the mechanical stops that limit the maximum advance. To set the limit, you
remove the Unilite plate and vacuum advance mechanism, if so equipped. There
are two allen head set screws that screw into the side of the distributor
housing to retain the Unilite plate. They are quite small so look closely
for them and make sure not to lose them. Once the plate is out of the way,
there will be two stops, 180 degrees apart. You loosen the screws holding
the stops and then insert the Mallory stepped plastic key. Each step is
marked and corresponds to 2 degree advance increments. Insert the key to
the desired stop, push the stops in and tighten the retaining screws. Mallory
has a chart that that I've included below that shows the proper springs to
use with the advance limits chosen.
Some additional info from a web source on how to properly check the Mallory
wiring:
I often hear people ask what voltage they should have at the coil when running
a Mallory module without an external box. The standard answer is about 7 to 10
volts measured at the coil with the engine running. However, while this is easy
to measure, it is not the best thing to measure since the voltage will vary
depending on the voltage output of the alternator. What really matters is the
total resistance of the primary side of the ignition. This includes the ballast
(or resistor wire) and the primary resistance in the coil (measured with an ohm
meter between the positive and negative terminals on the coil). The ideal total
resistance is a minimum of 1.4 ohms and a maximum of about 3.5 ohms. More than
3.5 ohms is safe for the module but the spark may be too weak for optimum
performance. Use an ohm meter to measure the resistance across the ballast and
add that to the amount of primary resistance in the coil. The total should be
between 1.4 and 3.5 ohms. You may need to measure the resistance of the ballast
after it has warmed up since some ballast resistors increase in resistance with
temperature. If your car has a resistor wire rather than a ballast it can be
difficult to measure the resistance in the wire as the wire gets lost in the
harness. If so, assume that the resistance in the wire is about 1.0 ohms which
is typical.
Some coils have so much primary resistance that a ballast resistor or resistor
wire is not necessary. Mallory has two new Promaster coils that have all the
resistance built into the coil (29450 and 30450). Using these coils, no
additional resistance is needed.
Having all the resitance built into the coil has drawbacks however. The coil
will run hotter which will reduce the life of the coil somewhat. Also, high
resistance coils are not recommended for use with external boxes as the coils
will overheat and fail (sometimes even explode!).
Advance spring selection instructions (thankfully typed in by Kirby Schraeder)
There are two basic advance curve configurations; the Straight-Line Curve
and the Hop-Out Curve. The Straight-Line Curve is used when a smooth linear
advance is required throughout the engine operating RPM. The Hop-Out Curve
is used when a lot of advance is required early and a more gradual advance
through the rest of the engine operating RPM.
1. The first step is to decide which curve will best suit your particular
application. This will all be determined by engine RPM operating range, type
of use and engine components used. For figuring Straight-Line Curve, use
steps 2 through 5. For figuring Hop-Out Curve, use steps 6 through 11.
2. In order to plot a Straight-Line Curve you must decide at what RPM you
want your advance to start and at what RPM you want your total advance to
finish. The curve in Figure 1 is an example, it starts at 1000 RPM and is
fully advanced at 2400 RPM. Plot your curve on the graph in Figure 3.
(Figure 1, 2 and 3 are all line graphs with the x-axis being engine rpm and
the y axis being degrees advance at the crankshaft.)
3. Mark off a 1000 RPM interval and count the number of degrees in that
interval. (The curve in Figure 1 of their chart has 19 degrees per 1000 rpm
interval because it starts at 1000 and ends up at 26 degrees advance at 2400
rpm. A little straight line y=mx+b math will give you the solution between
any other points.)
4. Using the Straight-Line Curve Chart, go down the Degree Column until you
come to the same number of degrees as you figured in step 3. The letters in
the Spring Column of what I sent previously will tell you which springs to
use. The springs they use in their example are A-B for 19 degrees.
The 'Hop-Out stuff' is a bunch more typing....
Initial will be around 16 degrees with a hot cam, with 10 at the distributor
(10 distributor = 20 crank degrees since the cam and distributor run at half
the crank speed) for a total advance of 36 degrees.
Mallory Unilite advance spring selection Table 1 shows:
Degrees Springs
7 degrees or less E-F
8 1/2 E-E
9 A-F
9 1/2 B-F
10 C-F
11 D-D
12 1/2 C-D
13 1/2 C-C
14 A-D
15 B-C
16 A-C
18 B-B
19 A-B
20 A-A
20-26 B
28 up A
Springs
A Red
B Blue
C Dark Green
D Bronze
E Black
F Light Green
G Orange
H Light blue
I Yellow
J Pink
K Silver
L White
> If you are employing a Crane retro-fit roller cam, you'll need to use
> Crane's steel gear designed for that application.
Crane advertises their gear is compatible with both iron and steel cam
cores. The also have an interesting 351C distributor that does the
mechanical and vacuum advance electronically. There are two dials
on the distributor that allow you to switch between a series of
different advance curves. Would be a nice touch in a Pantera.
Dan Jones
