MSD 62153 DIS-4 Plus High Output Installation - Manual (Page 2)

2 INSTALLATION INSTRUCTIONS
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THEORY OF OPERATION
CAPACITIVE DISCHARGE
The MSD Digital DIS Series Ignitions feature a capacitive discharge ignition design. The majority of
stock ignitions are inductive ignitions. In an inductive ignition, the coil must store and step up the
voltage to maximum strength in between each firing. At higher rpm, since there is less time to charge
the coil to full capacity, the voltage falls short of reaching maximum energy which results in a loss of
power or top end miss.
The MSD Ignition features a capacitor which is quickly charged to 460-480 volts and stores it until
the ignition is triggered. With the CD design, the voltage sent to the coil is always at full power even
at high rpm.
MULTIPLE SPARKS
The MSD Digital DIS Series Ignition produces full power multiple sparks for each firing of the spark
plug. The number of sparks that occur decreases as rpm increases, however the spark series always
lasts for 20° of crankshaft rotation. Above 3,000 rpm there is simply not enough time to fire the spark
plug more than once, so there is only one powerful spark.
REV LIMITER
The MSD DIS-2 and 4 Ignitions are equipped with a built-in adjustable Soft Touch Rev Control. This
rev limit feature can be adjusted in 100 rpm increments using the program switches on the ignition's
end panel. The Soft Touch circuitry provides a smooth and accurate rev limit by dropping the spark
to individual cylinders. The Soft Touch produces a load-free rev limit that is accurate to within 10 rpm
of the selected rpm.
GENERAL INFORMATION
BATTERY
An MSD Digital DIS Series Ignition will operate on any negative ground, 12 volt electrical system
without a distributor. The MSD can be used with a 16 volt battery and can withstand a momentary 24
volts in case of a jump start. The ignition will deliver full voltage with a supply of 12 - 18 volts and will
operate with a supply voltage as low as 8 volts.
If your application does not use an alternator, allow at least 15 amp/hour for every half hour of operation.
If the engine is cranked with the same battery or other accessories such as an electric fuel pump, fan
or water pump are used, the amp/hour rating of the battery must be increased.
COILS
The MSD Digital DIS Ignitions can be used with most stock coils and most aftermarket coils that are
designed to replace the stock coils. If you have any questions concerning coils, contact our MSD
Customer Service Department at (915) 855-7123. Due to the increased energy driving the stock coils,
this ignition should not be used for street use.
TACHOMETERS/FUEL INJECTION
The MSD Digital Series Ignitions feature a Tach Output Terminal on the side of the unit. This terminal
provides a trigger signal for tachometers, fuel injection, a shift light or other add-on devices that require
a 12 volt square wave rpm signal with a 20° duration.
Some vehicles may require an Ignition Adapter to operate properly with the MSD. For more information
on tachometers and MSD Ignition Adapters, refer to page 13.
NOTE: If you plan on welding on your vehicle, to avoid possible damage to the ignition, always
disconnect both MSD Heavy Power cables from the battery. It is also recommended that the
tach ground wire be disconnected.