MSD 8485 Installation

MSD Billet VW Distributor

PN 8485

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Important:  Read these instructions before attempting the installation.

Parts Included:

1- Billet Distributor
2 - #10 Disc Washers
3 - Advance Stops
1 - Retaining Nut
7 - Shims

TIMING FUNCTIONS

Before continuing with the installation, here are a few definitions you should be aware of:

Initial Timing: This is the base timing of the engine before centrifugal advance begins.

1 - Clamp Stud
4 - Advance Springs
1 - Hold Down Bracket
2 - O-Rings

Centrifugal Advance: The centrifugal advance mechanism is made up of weights, springs, advance 
cam, 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.

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.

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

FACTOR Advance Timing Retard Timing
For For

Cylinder Pressure  Low  High
RPM  High  Low
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 11.5:1compression, a high energy ignition and turns 5,500 rpm. With the 
specifications given, you will have to retard the timing for the high compression, low rpm 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 2 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 or engine 
kick-back.

•  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

Figure 2 Advance Curves.

CENTRIFUGAL ADVANCE CURVE

The centrifugal advance mechanism is made up of weights, springs, an advance cam and the advance 
stop bushing. The distributor can be used in a wide selection of applications by changing only the 
springs and the advance stop bushing. There is no need to change the weights or advance cam.

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. 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.

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