PN 83891 - 392 Early Hemi
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P a r t s I n c l u d e d:
1 - Pro-Billet Distributor
1 - Rotor, PN 8467
1 - Distributor Cap, PN 8433
1 - Wire Retainer
2 - 1.5" Self Tapping Screws
2 - 10-32 x 3/4" Socket Head Screws
MSD Pro-Billet
Chrysler Distributor
1 - Advance Kit
1 - O-Ring
1 - Vacuum Advance Lock-Out Kit
WARNING:
Before installing the MSD Distributor, disconnect the battery cables. When disconnect-
ing the battery cables, always remove the Negative (-) cable first and install it last.
Note:
The terminals of this Distributor require spark plug style terminals. You may need to change the
terminals and boots of your wires. MSD offers two kits, PN 8849 or PN 8848 that are supplied with
nine boots and terminals.
TIMING FUNCTIONS
Before continuing with the installation, here are a few definitions you should be aware of:
Initial Timing:
This is the base timing (also referred to as idle timing) of the engine before the
centrifugal advance begins.
Centrifugal Advance:
The centrifugal (or mechanical) advance mechanism is made up of weights,
springs, advance cams, and an advance stop bushing. The amount and rate of advance that your
distributor is capable of is determined by the centrifugal timing. If you ever wish to lock out the
centrifugal advance, refer to the centrifugal advance section.
Total Timing:
This is the total of the initial timing plus the centrifugal advance added together.
Example: 10° Initial + 25° centrifugal = 35° Total Timing. (When checking Total timing, disconnect
and cap the vacuum canister and plug the vacuum line.)
Vacuum Advance:
The vacuum advance will advance the timing up to approximately 12° during
partial throttle driving (with 15 lbs of vacuum). The vacuum line should be routed to a ported vacuum
outlet above the throttle plates.
Note:
MSD Distributors are supplied with the heavy (slow) advance springs and the 21° stop bushing
installed. This is to prevent detonation in certain applications. Review the information on pages
2-4 to determine the best advance curve for your application.
MSD
•
WWW.MSDPERFORMANCE.COM
• (915) 855-7123 • FAX (915) 857-3344
2
INSTALLATION INSTRUCTIONS
CHOOSING AN ADVANCE CURVE
The function of the advance curve is to match the ignition timing to the burning rate of the fuel and
speed (rpm) of the engine. Any factor that changes the burning rate of the fuel or the engine speed
can cause a need for an ignition timing change. Figure 1 shows some of the factors that will affect
engine timing.
FACTOR
Cylinder Pressure
Vacuum
Energy of Ignition
Fuel Octane
Mixture (Air/Fuel)
Temperature
Combustion Chamber Shape
Spark Plug Location
Combustion Turbulence
Load
Advance Timing
For
Low
High
Low
High
Rich
Cool
Open
Offset
Low
Light
Figure 1 Ignition Timing Factors.
Retard Timing
For
High
Low
High
Low
Lean
Hot
Compact
Center
High
Heavy
As you can see from the chart, most factors will change throughout the range of the engine operation.
The timing mechanism of the distributor must make timing changes based on these factors.
Example:
An engine has 11:1 compression with a high energy ignition. With the specifications given,
you will have to retard the timing for the high compression and high energy ignition. By comparing
the engine’s specifications against the chart, a usable timing guideline can be found. Engines with
a combination of items from both columns will require a timing that is set in the mid range.
Obviously a full technical explanation of correct ignition timing would be very complicated. The best
way to arrive at a suitable ignition curve for your engine is to use the Ignition Timing Factors Chart
as a guide and compare it to the Advance Graphs in Figure 4 until a suitable curve is found. When
selecting your advance curve, use detonation (engine ping) as an indicator of too much advance,
and a decrease in power as an indicator of too little advance.
TIPS ON SELECTING AN ADVANCE CURVE
• Use as much initial advance as possible without encountering excessive starter load.
• Start the centrifugal advance just above the idle rpm.
• The starting point of the centrifugal advance curve is controlled by the installed length and
tension of the spring.
• How quickly the centrifugal advance (slope) comes in is controlled by the spring stiffness. The
stiffer the spring, the slower the advance curve.
• The amount of advance is controlled by the advance bushing. The bigger the bushing, the
smaller the amount of advance.
CENTRIFUGAL ADVANCE CURVE
SELECTING THE ADVANCE SPRINGS
The rate, or how quick the advance comes in is determined by the type of springs which are installed
on the distributor. The MSD distributors are equipped with two Heavy Silver springs installed. These
will give you the slowest advance curve possible (Figure 2). The parts kit contains two additional sets
of springs which can be used to match the advance curve to your particular application. Refer to the
Spring Combination Chart (Figure 3) for combinations that can be achieved.
To change the springs, remove the cap and rotor and use needlenose pliers to remove the springs.
Be sure the new springs seat in the groove on the pin.
MSD
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INSTALLATION INSTRUCTIONS
3
Timing Curve From Factory
SPRING COMBINATION
2- Heavy Silver
1- Heavy Silver
1- Light Blue
1-Heavy Silver
1-Light Silver
2- Light Blue
1- Light Silver
1- Light Blue
2- Light Silver
RATE OF ADVANCE
SLOWEST
FIGURE 4
A
B
C
D
E
FASTEST
F
Figure 2 The Factory Equipped Curve.
Figure 3 Spring Combination Chart.
ADVANCED
STOP BUSHING
RED
SILVER
GREEN
BLUE
PURPLE
BLACK
ADVANCED
STOP BUSHING
RED
SILVER
GREEN
BLUE
PURPLE
BLACK
ADVANCED
STOP BUSHING
RED
SILVER
GREEN
BLUE
PURPLE
BLACK
ADVANCED
STOP BUSHING
RED
SILVER
GREEN
BLUE
PURPLE
BLACK
ADVANCED
STOP BUSHING
RED
SILVER
GREEN
BLUE
PURPLE
BLACK
ADVANCED
STOP BUSHING
RED
SILVER
GREEN
BLUE
PURPLE
BLACK
Figure 4 Advance Curves.
MSD
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4
INSTALLATION INSTRUCTIONS
BUSHING SIZE
Red-Smallest
Silver
Green
Blue
Purple
Black-Largest
APPROXIMATE
CRANKSHAFT
DEGREES
28
25
23
21
19
18
SELECTING THE ADVANCE STOP
BUSHING
Five different advance stop bushings are supplied
in the distributor kit. The distributor comes with a
Blue (21°) bushing already installed. If a different
amount of centrifugal advance is desired, follow the
next procedure to change the bushings. The chart
in Figure 5 gives the size and approximate degrees
for the corresponding bushings.
CHANGING THE ADVANCE STOP
BUSHINGS
Figure 5 Advance Stop Bushing Chart.
1. Remove the distributor cap and rotor.
2. Remove the locknut and washer on the bottom
of the advance assembly (Figure 6).
3. Remove the bushing and install the new one.
Install the washer and locknut.
LOCKING OUT THE CENTRIFUGAL
ADVANCE
Figure 6 Changing the Advance Stop Bushing.
1. Remove the advance components including the
springs, weights and the advance stop bushing
from the advance assembly.
2. Remove the roll-pin from the shaft and slide the
retaining sleeve down, (Figure 7).
3. Slide the shaft two inches out of the housing.
4. Rotate the shaft 180° and insert the advance stop
bushing pin into the small hole on the advance
plate (Figure 8).
5. Install the locknut and washer to the advance stop
bushing pin. This locks the advance in place.
6. Install the retaining sleeve and roll-pin.
Note:
If you want to lock out the vacuum advance,
see page 6.
Figure 7 Removing the Retaining Sleeve.
Figure 6 Locking Out the Centrifugal Advance.
Figure 8 Locking Out the Advance.
MSD
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INSTALLATION INSTRUCTIONS
5
INSTALLING THE DISTRIBUTOR
1. Remove the existing distributor cap without
disconnecting any of the spark plug wires.
2. With the cap off, crank the engine until the
rotor is aimed at a fixed point on the engine or
firewall. Note this position by making a mark
(Figure 9).
3. Place the distributor cap back on and note
which plug wire the rotor is pointing to. MARK
THE SPARK PLUG WIRES and remove the
distributor cap.
4. Disconnect the wiring from the distributor.
5. Loosen the distributor hold down clamp,
slide the clamp out of the way and lift the
distributor out of the engine.
6. Install the new O-ring and install the new
distributor making sure that the rotor
comes to rest pointing at the fixed mark.
If the distributor will not fully seat with the
rotor pointing to the marked position, you
may need to rotate the oil pump shaft until
the rotor lines up and the distributor fully
seats.
7. Position and tighten the hold down clamp
onto the distributor.
8. Install the distributor cap and spark plug
wires one at a time to ensure correct
location. An optional wire retainer is
supplied to secure the wires in place. Align
the mounting bosses and use the supplied
1.5" self-tapping Phillips screws to hold the
retainer in place.
Figure 9 Marking the Rotor Location.
Installation Option:
This Cap can also be
bolted down to an MSD Pro-Billet or Billet
Distributor base with the supplied hardware.
To accomplish this, the spring clips must be
cut off (Figure 10).
Note:
When the cap is bolted down, the
location of the spark plug wires must
be changed.
Figure 10 Optional Installation by Bolting Cap Down.
MSD
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• (915) 855-7123 • FAX (915) 857-3344
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