2
INSTALLATION INSTRUCTIONS
AUTOTRONIC CONTROLS CORPORATION
• 1490 HENRY BRENNAN DR., EL PASO, TEXAS 79936 • (915) 857-5200 • FAX (915) 857-3344
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.
