MSD 8394 Installation

MSD Pro-Billet Digital E-Curve Distributor

PN 8394 - U.S. Patent 6820602

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Important:  Read these instructions before attempting the installation.

Pa r ts In c lu d ed :

1 - Digital E-Curve Distributor
1 - Rotor, PN 8467
1 - Distributor Cap, PN 8433
1 - Wire Retainer
2 - 1.5" Self Tapping Screws

WARNING: Before installing the MSD Digital E-Curve Distributor, disconnect the battery cables. 

When disconnecting the battery cables, always remove the Negative (-) cable first 
and install it last.

Note:  The terminals of this Digital E-Curve 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.

Note:  If the gear is ever replaced, MSD Gear (PN 8531) 

is  required  for  replacement  due  to  the  .500" 
diameter shaft.

DIGITAL E-CURVE FUNCTIONS

1 - 3-Pin Harness
1 - Gasket
1 - Tube of Gear Lubricant
2 - O-Rings
1 - Timing Tape Set, PN 8985

Rev

Limiter

RPM LIMIT

This distributor is equipped with an adjustable rev limiter. It 
is adjustable from 5,000 - 10,000 rpm by a rotary dial under 
the cap and rotor (Figure 1). The rpm will not exceed your 
selected amount to protect the engine from overrev damage.

Figure 1 Rotary Dial Adjustments.

Timing

Switch 1

Timing Switch 2

TIMING FUNCTIONS

Electronic Advance Curve Operation: The Electronic Advance Curve is managed by a microprocessor 
built into the ignition module. You can program an electronic timing advance curve by adjusting two 
rotary switches under the distributor cap (Figure 1). A magnetic pickup is used as a trigger device 
that tells the ignition module when to fire the coil. The pickup is triggered by a reluctor mounted to 
the distributor shaft. This means that you have to set the distributor at the highest, or Total, amount 
of advance that you want to achieve (including vacuum advance) and compensate with one of the 
selectable ignition curves (shown on page 4). Following are important definitions that will be used to 
set up your timing.

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2 INSTALLATION INSTRUCTIONS

Electronic Centrifugal Advance: Since this distributor is all electronic, there really is no mechanical 
or centrifugal advance. On a standard distributor, this advance would be called centrifugal so it will 
be referred to as the electronic  centrifugal  advance. The chart on page 4 shows all of the different 
combinations you can achieve by simply turning the two rotary dials located under the distributor cap.

Total Timing: This is the total amount of timing that the engine will achieve. This is the amount that 
all of the electronic curve and settings will be based from. This setting also includes any amount of 
vacuum advance that you plan to use.

Vacuum Advance: The vacuum advance will advance the timing under part throttle conditions when 
the engine is not under a heavy load. This advance is added on to the electronic timing curve as 
well. The advance will begin as low as 4-in. of vacuum and will max out at 10-in. of vacuum. There is 
a separate chart in Figure 3 that illustrates the vacuum curve selection.

Locked-Out Timing: If you do not want to have a timing advance, set the rotary dials in the Locked­Out position. This means the timing will not move from the setting you position the distributor in. You 
may however, take advantage of a start retard (see below).

Start Retard: When you select Locked-Out timing, the engine may be hard to crank. A start retard 
amount can be selected to aid in cranking. This amount can range from 5°, 10°, 15° and 20°. When 
the engine is cranking, the timing will be retarded. Once the engine reaches 600 rpm, the timing will 
return to the locked-out setting.

Note:  The total  amount  of any  timing change  that  can be  achieved  is 34°  (25° for  the  electronic 

advance with vacuum an additional 9°). This includes the electronic advance as well as the 
vacuum advance.

Note:  It is recommended to have a dial-back timing light, timing tape or a fully degreed balancer to 

set the timing correctly. 

CHOOSING AN ADVANCE CURVE

The function of the advance curve is to match the ignition timing to the burning rate of the fuel with 
the speed (rpm) of the engine.  The piston is traveling much faster through the combustion stroke at 
5,000 rpm compared to 1,000 rpm. Any factor that changes the burning rate of the fuel or the engine 
speed can cause a need for an ignition timing change.  Figure 2 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 2 Ignition Timing Factors.

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INSTALLATION INSTRUCTIONS 3

As you can see from the chart, most factors will change throughout the range of the engine operation. 
The Digital E-Curve allows you to make timing changes based on these factors.

Example:  An engine has 11:1 compression, a high energy ignition and turns 5,500 rpm.  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 3 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. Also consider how the engine cranks and 
starts. Too much advance can cause an engine to crank slow or even kick back. Here are a couple 
of suggestions.

•  Use as much initial advance as possible without encountering excessive starter load.

•  Start the electrical advance just above the idle rpm.

•  Select an advance curve that produces good acceleration without detonation.

SETTING UP THE DISTRIBUTOR

Rotate the engine to TDC then to 12° - 15° BTDC. With the rotary switches set to "1" and "7" (These 
settings will be used to start the engine and adjusted later.) install the distributor with th rotor pointing 
to the number 1 spark plug wire and start the engine.

With the engine running and a timing light connected, adjust the timing to the desired Total Timing. 
(Example 32°  without  vacuum  advance)  Once you've  set the  total  timing, turn  the engine  off  and 
remove the distributor cap. Set the rotary dials to achieve the desired timing curve (Figure 3 and 4).

For example  with total timing set at 32° and the rotary dials set to "2" and "9". The engine  will  idle 
at 12°, timing will start to advance at 1,100 rpm and will be fully advanced by 3,500 rpm, plus a 15° 
vacuum advance at 10 in-Hg (inches of vacuum).

If your balancer does not have any timing marks, MSD offers timing tape kit PN 8985.

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