MSD 8365 Installation

MSD Pro-Billet Chevrolet HEI Distributor

PN 8365

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Important: Read these instructions before attempting the installation.

Parts Included:

1 - Pro-Billet Distributor, PN 8365
1 - Rotor, PN 84101
1 - Distributor Cap, PN 84111
1 - Coil Cover, PN 84022
1 - Digital HEAT Module, PN 83647
1 - Coil, PN 8225
1 - Advance Kit
1 - Gasket

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.

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.

1 - Tube of Gear Lubricant
1 - Vacuum Advance Lock-Out
2 - O-rings
1 - HEI Connector
2 - HEI Wiring Terminals
1 - HEI/Tach Connector
1 - Vacuum Advance Adjusting Kit
1 - Gray Tach Wire

Centrifugal Advance: The centrifugal (or mechanical) advance mechanism is made up of weights,
springs 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.

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.

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
the vacuum canister and plug the vacuum source.)

Vacuum Advance: The vacuum advance will advance the timing up to 10° during partial throttle
driving (with 15 lbs of vacuum). The vacuum line should be routed to a ported vacuum outlet above
the throttle plates.

RPM LIMIT AND TACHOMETER INFORMATION

Tach Signal: The Pro-Billet HEI Distributor features a Gray Tach Output wire which provides a clean signal

for most tachometers and even some aftermarket fuel injection systems. The signal output
is a 12 volt square wave, 20° duty cycle. This wire is also responsible for programming the
built-in rev limiter.

M S D   •   W W W . M S D P E R F O R M A N C E . C O M   •   ( 9 1 5 )   8 5 7 - 5 2 0 0   •   F A X   ( 9 1 5 )   8 5 7 - 3 3 4 4

2 INSTALLATION INSTRUCTIONS

PROGRAMMING THE REV LIMIT

The rev limiter of the HEAT module requires a tachometer to set the rev limit. The limit is programmed by running
the engine at half the desired rpm, then momentarily grounding the Gray tach output wire from the MSD. A
Gray jumper wire is supplied to connect to the tach with another tee-splice coming off to use for programming.
A switch may also be installed to ease adjustments of the limiter. The default rpm limit is 10,000 rpm.

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 Advance Timing Retard Timing
For For

Cylinder Pressure Low High
Vacuum High Low
Energy of Ignition Low High
Fuel Octane High Low
Mixture (Air/Fuel) Rich Lean
Temperature Cool Hot
Combustion Chamber Shape Open Compact
Spark Plug Location Offset Center
Combustion Turbulence Low High
Load Light Heavy

        Figure 1 Ignition Timing Factors. 

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.

M S D   •   W W W . M S D P E R F O R M A N C E . C O M   •   ( 9 1 5 )   8 5 7 - 5 2 0 0   •   F A X   ( 9 1 5 )   8 5 7 - 3 3 4 4

INSTALLATION INSTRUCTIONS 3

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.

Timing Curve From Factory

Figure 2 The Factory Equipped Curve. 

SPRING COMBINATION RATE OF ADVANCE FIGURE 4

2- Heavy Silver SLOWEST A
1- Heavy Silver B
1- Light Blue
1-Heavy Silver C
1-Light Silver
2- Light Blue D
1- Light Silver E
1- Light Blue
2- Light Silver FASTEST F

Figure 3 Spring Combination Chart. 

Figure 4 Advance Curves.

M S D   •   W W W . M S D P E R F O R M A N C E . C O M   •   ( 9 1 5 )   8 5 7 - 5 2 0 0   •   F A X   ( 9 1 5 )   8 5 7 - 3 3 4 4