6421 Datasheet, PDF (3/28 Pages) Mallory performance club – The MSD produces full power multiple sparks for each firing of a plug

INSTALLATION INSTRUCTIONS
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Routing: Correct routing of the plug wires is also important to performance. Wires should be routed
away from sharp edges and engine heat sources. If there are two wires that are next to each other in
the engine’s firing order, the wires should be routed away from each other to avoid inducing a spark
into the other wire. For example, in a Chevy V8, the firing order is 1-8-4-3-6-5-7-2. The #5 and #7
cylinders are next to each other in the engine and in the firing order. If the voltage from the #5 wire
is induced into #7 detonation could occur and cause engine damage.
To add more heat protection to your plug wires, MSD offers Pro-Heat Guard, PN 3411. This is a glass
woven and silicone coated protective sleeve that you slide over your plug wires. For extra protection
of the spark plug boots, MSD offers Pro Boot Guard, PN 3412.
Spark Plugs: Choosing the correct spark plug design and heat range is important when trying to get
the best performance possible. Since there are so many engine combinations and manufacturers,
MSD does not recommend which plug or gap is exactly right for your application.
It is recommended to follow the engine builder or manufacturer’s specification for spark plugs. With
that, you can then experiment with the plug gap to obtain the best performance. The gap of the plugs
can be opened in 0.005" increments, then tested until the best performance is obtained. MSD judges
the plug gap by compression and components.
Compression Spark Plug Gap
These examples are just starting points to get you going
in the right direction. Every application is different and
Up to 10.5:1: 0.035" - 0.045"
10.5:1 - 13.0:1: 0.030" - 0.035"
should be tested and tuned.
Above 13.0:1: 0.025" - 0.030"
Note: Close the spark plug gap down as compression increases.
Welding: If you are welding on your vehicle, to avoid the chance of damage, always disconnect both
Heavy Power cables of the MSD (You should also disconnect the tach ground wire too).
Distributor Cap and Rotor: It is recommended to install a new distributor cap and rotor when installing
the MSD Ignition Control. The cap should be clean inside and out especially the terminals and rotor tip.
On vehicles with smaller caps, it is possible for the air inside the cap to become electrically charged
causing crossfire which can result in misfire. This can be prevented by drilling a couple vent holes in
the cap. The holes should be placed between the terminals, at rotor height and face away from the
intake. If your environment demands it, place a small piece of screen over the hole to act as a filter.
MOUNTING
The MSD can be mounted in the engine compartment as long as it is away from direct engine heat
sources. It is not recommended to mount the unit in an enclosed area such as the glove box.
When you find a suitable location to mount the unit, make sure the wires of the ignition reach their
connections. Also be sure that the program dials can be accessed. Hold the Ignition in place and
mark the location of the mounting holes. Use a 3/16" bit to drill holes, install the vibration mounts and
mount the ignition.
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