MSD 8504 Chrysler, 318, 340, 360, E-Curve Distributor Installation - Manual (Page 2)

2 INSTALLATION INSTRUCTIONS
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• 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
Figure 2 Ignition Timing Factors.
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
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.