MSD 8573 Flathead Ford Ready to Run Distributor for '49-'53 Installation - Manual (Page 2)

2 INSTALLATION INSTRUCTIONS
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
RPM LIMIT AND TACHOMETER INFORMATION
Tach Signal: The Ready-to-Run Distributor features a Gray Tach Output wire which provides a clean signal
for most tachometers and even some aftermarket fuel injection systems. The signal output
is a 12 volt square wave, 20° duty cycle. This wire is also responsible for programming the
built-in rev limiter.
Rev Limiter: The Ready-to-Run Distributor has a built-in rev limit that can easily be adjusted from 2,000
rpm to over 10,000 rpm. The default is 10,000 rpm. To set the rev limiter, run the engine to half
the desired rpm then ground the Gray Tach wire (a jumper is supplied) for approximately one
second. Every time the key is turned to the On position, the tach will display the programmed
rpm limit. See page 8 for the programming procedure.
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.
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 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 11:1 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 4 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.
• 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.