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.

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4 INSTALLATION INSTRUCTIONS

Figure 3 Available Timing Curves.

Figure 4 Advance Curve Switch Position.

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INSTALLATION INSTRUCTIONS 5

INSTALLING THE DISTRIBUTOR

Note: When installing the distributor for the first time, it is recommended to place the switches in 

the locked-out timing  position. This will assist you in setting the  timing curve by ensuring 
that the total timing is correct.

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 5).

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 
and slide the clamp out of the way.

6. Lift the distributor out of the engine.   Note 
that the rotor rotates as you lift the distributor 
out. This is due to the helical cut gear and 
should be taken into  consideration  when 
installing the new distributor.

7. Install the gasket and apply a liberal amount 
of the supplied lubricant to the distributor 
gear. (The  supplied O-rings can  only  be 
used  if  the  block  has  been  modified  as 
shown in Figure 6.)

8. Install the 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.

9. Position and tighten the hold down clamp 
onto the distributor.

10. Install  the  distributor  cap and spark plug 
wires  one  at  a  time  to  ensure  correct 
location.  A  wire  retainer  is  supplied  to 
secure  the  wires  in  place.  A lign  the 
mounting  bosses  and  use  the  supplied

1.5"  self-tapping  Phillips  screws  to  hold  
the retainer in place.

11. Proceed to wiring the distributor as shown in Figures 7 and 8. Review the starting and tuning tips 
information and install the Timing Tape as shown on page 7 before starting the engine.

Figure 5 Marking the Rotor Location.

Figure 6 Modified Block for use with O-Rings.

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6 INSTALLATION INSTRUCTIONS

RED

ORANGE

BLACK

*MUST BYPASS THE BALLAST RESISTOR.

TO COIL POSITIVE + 12 VOLTS

TO COIL NEGATIVE

TO ENGINE GROUND

-

Figure 7 Wiring the Ready-to-Run Chevrolet Distributor.

NOTE: THE DIGITAL E-CURVE DISTRIBUTORS DO NOT

REQUIRE AN MSD IGNITION, THOUGH THEY CAN
BE USED WITH ONE. THE TIMING CURVE AND
RPM LIMIT WILL STILL FUNCTION.

*MUST BYPASS THE
BALLAST RESISTOR.

Figure 8 Connecting an MSD Ignition Control to the Digital E-Curve Distributor.

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INSTALLATION INSTRUCTIONS 7

INSTALLING THE TIMING TAPE

1. Locate the top-dead center or 0°  mark on the harmonic 
balancer or timing wheel.

2. Select the correct timing tape for your application. Make 
sure you know the correct size of the harmonic balancer 
or timing wheel you’re using. If this is not known, measure 
the diameter of the harmonic balancer or timing wheel’s 
edge and note the size.

3.  Choose  the  timi ng  tape  that  matches  you r  balancer’s 
diameter. Be sure that the mating surface is clean of any 
dirt, grease or debris. Locate and note the 0° mark on the 
timing tape.

4. Align the 0°  mark on the tape with the TDC  mark on the 
balancer. Make  sure  that  the  markings on  the tape  are 
facing you, and place the tape on the surface. Use firm 
pressure for proper adhesion. ATC (after top-dead center) 
will  be  to  the  l eft  of  the  stock  mark,  and  BTC  (before 
top-dead center) will always be to the right of the stock 
mark.

Figure 9 The Timing Tape Installed.

ZERO

DEGREE

(TDC)

STARTING AND TUNING TIPS

•  Position the rev limiter rotary dial at your desired rpm limit. 

•  At this point, the distributor should be installed at your  desired timing and wired to the coil, and 
ground.

•  It is recommended that you have a dial-back timing light or degreed balancer. MSD offers a timing 
tape that you can apply to your balancer as PN 8985.

•  Select a Locked-Out with Start Retard to start the engine (These are Curves Q, R, S or T). This way 
you can position the distributor to obtain your ideal total timing before selecting a timing curve.

•  If you are going to use a vacuum advance curve, use a 3/16" vacuum line connected to ported 
vacuum.  This  means  a  vacuum  source  that  is  above  the  throttle  plates.  Also,  remember  to 
disconnect and plug the vacuum line when setting the timing curve.

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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 the Cap Down.

Service

  In case of malfunction, this MSD component will be repaired free of charge according to the terms of the warranty. 

When returning MSD components for warranty service, Proof of Purchase must be supplied for verification. After 
the warranty period has expired, repair service is based on a minimum and maximum fee.

All returns must have a Return Material Authorization (RMA) number issued to them before 

being returned. To obtain an RMA  number please contact  MSD Customer Service at 1 (888) MSD-7859 or  visit 
our website at  www.msdperformance.com/rma to  automatically obtain a  number  and  shipping information.

When returning the unit for repair, leave all wires at the length in which you have them installed. Be sure to include 
a detailed account of any problems experienced, and what components and accessories are installed on the vehicle. 
The repaired unit will be returned as soon as possible using Ground shipping methods (ground shipping is covered 
by warranty). For more information, call MSD at [phone]. MSD technicians are available from 7:00 a.m. to 
5:00 p.m. Monday - Friday (mountain time).

Limited Warranty

  M

SD warrants this product to be free from defects in material and workmanship under its intended normal use*, 
when properly installed and purchased from an authorized MSD dealer, for a period of one year from the date of 
the original purchase. This warranty is void for any products purchased through auction websites. If found to be 
defective as mentioned above, it will be repaired or replaced at the option of MSD. Any item that is covered under 
this warranty will be returned free of charge using Ground shipping methods. 
  This shall constitute the sole remedy of the purchaser and the sole liability of MSD. To the extent permitted by 
law, the foregoing is exclusive and in lieu of all other warranties or representation whether expressed or implied, 
including any implied warranty of merchantability or fitness. In no event shall MSD or its suppliers be liable for special 
or consequential damages.
  *Intended normal use means that this item is being used as was originally intended and for the original application 
as sold by MSD. Any modifications to this item or if it is used on an application other than what MSD markets the 
product, the warranty will be void. It is the sole responsibility of the customer to determine that this item will work for 
the application they are intending. MSD will accept no liability for custom applications.

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

© 2012 Autotr onic Con trols Corporat ion

FRM30102 Revised 01/12 Printed in U.S.A.